- ALT_1 Introduction to ecosystems Introduction to ecosystems If reading this text has inspired you to learn more, you may be interested in joining the millions of people who discover our free learning resources and qualifications by visiting The Open University [http://www.open.ac.uk/choose/ou/open-content]. Copyright © 2014 The Open University Except for third party materials and/or otherwise stated (see terms and conditions [http://www.open.ac.uk/conditions]) the content in OpenLearn and OpenLearn Works is released for use under the terms of the Creative Commons Attribution-NonCommercial-Sharealike 2.0 licence [http://creativecommons.org/licenses/by-nc-sa/2.0/uk/]. In short this allows you to use the content throughout the world without payment for non-commercial purposes in accordance with the Creative Commons non commercial sharealike licence. Please read this licence in full along with OpenLearn terms and conditions before making use of the content. 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These are: OU logos, trading names and may extend to certain photographic and video images and sound recordings and any other material as may be brought to your attention. Unauthorised use of any of the content may constitute a breach of the terms and conditions and/or intellectual property laws. We reserve the right to alter, amend or bring to an end any terms and conditions provided here without notice. All rights falling outside the terms of the Creative Commons licence are retained or controlled by The Open University. Head of Intellectual Property, The Open University Week 1: What is an ecosystem? Introduction Throughout this course you will be considering these overarching questions: What is the importance of understanding ecosystems? How do they work? How crucial is their conservation? We start by defining the term ‘ecosystem’. Before we can begin to tackle the larger issues of ecosystems and how they have been compromised by human intervention, we must understand what is meant by ‘ecosystem’. By the end of this first week you will be able to explain how an ecosystem is defined, in terms of energy flow, and be able to define and use terms which are introduced in the videos and text and apply them to new situations and examples where appropriate. There is more than one way in which an ecosystem can be defined. In the following video Dr Mike Gillman highlights the difference between two schools of thought. One definition is that an ecosystem is an area where groups of organisms experience similar conditions. Alternatively, an ecosystem is a living system of energy transfer, a whole complex of organisms living together, linked by energy transfer. The key difference is that ‘area’ defines one, whereas ‘energy relationships’ define the other. As you watch ‘What is an ecosystem?’, consider the following questions, which we will discuss in the next section: What is the key difference between the definitions? What is the working definition of ‘ecosystem’ that we are going to use in this course? What is an ecosystem? DR MICHAEL GILLMAN Ecosystem-- what is it? What does it mean? How can we define what an ecosystem actually is? Well, there are two ways of doing it-- two definitions, two schools of thought. In the red corner, supporters of a geographical definition. They would say that an ecosystem is an area where groups of organisms experience similar conditions. These guys talk about the rainforest ecosystem, the Arctic ecosystem, that sort of thing. Defined like this, ecosystems tend to be, well, big. It's a widely used definition. You'll have heard politicians talk about ecosystems like that. And conservation groups tend to do the same thing. On the other hand, over here in the blue corner are people who prefer a different definition. These people say, it's not just an area, it's a living system of energy transfer, of nutrients being passed up and passed on. It's all about the system itself, not the box it comes in. This is the approach that would have been favoured by one of the founding fathers of the science of ecology, Sir Arthur Tansley. His view of an ecosystem revolved around his concept of the biome, which we would today call a community. He saw a community as being— NARRATOR "the whole complex of organisms naturally living together, whose life must be considered and studied as a whole." DR MICHAEL GILLMAN: Tansley's main interest was in plants, so his work and ideas tend to focus on them. He defined plant communities as-- NARRATOR "--any collection of plants growing together which has a whole certain individuality." DR MICHAEL GILLMAN Tansley's ideas were controversial and much debated. But they found favour in North America and Europe and, today, form the basis of the British National Vegetation Classification. The key thing is Tansley's ideas of communities were not just about geographical location. They were about how species interact together. And so was born Tansley's definition of an ecosystem. NARRATOR "A wider conception still is to include, with the biome, all the physical and chemical factors of the biome's environment, or habitat, as parts of one physical system which we may call an ecosystem, because it's based on the oikos, or home, of a particular biome. All the parts of such an ecosystem, organic and inorganic, biome and habitat, may be regarded as interacting factors." DR MICHAEL GILLMAN So there it is. That's what we mean by an ecosystem. And for the purposes of this course, we'll define ecosystem as-- NARRATOR "--a set of organisms and abiotic components, linked by processes of energy transfer and cycling of materials." DR MICHAEL GILLMAN And that, I reckon, is a win for the blue corner. Before you start, The Open University would really appreciate a few minutes of your time to tell us about yourself and your expectations of the course. Your input will help to further improve the online learning experience. If you’d like to help, and if you haven't done so already, please fill in this optional survey. 1.1 Define an ecosystem You should now be able to provide definitions of the key terms you have encountered in the previous video. Begin to construct your personal glossary of them, which you can keep by you as you study. Building your own glossary is an effective way of consolidating your learning. We have provided a Glossary template which you can use to build your own if you choose. There are already a few entries in the Glossary, to give you a feel for the sort of definitions that you should be including. But whatever method you choose for collecting together terms and definitions, by the end of your study of ecosystems you should have a working document that you can add to if you study other science subjects. To formulate a working definition of an ecosystem you may have to use some of the terms you have added to your glossary. Is the following definition a suitable one to work with? An ecosystem is a set of organisms and abiotic components linked by processes of energy transfer and cycling of materials. 1.2 Investigating ecosystems Let’s examine the concept of an ecosystem in more detail using an example that is familiar to many people: a pool on a rocky beach, in Britain (Figure 2). As you work through, consider what defines the limits of a particular ecosystem. How does the tide change the nature of a rock pool ecosystem? What role does the Sun take in sustaining the ecosystem in the rock pool? Also think about how can this be extrapolated and applied to other ecosystems with variable physical environments. 1.2.1 The rockpool Like all ecosystems, a rock pool is linked to the wider world and to other ecosystems. This link is most apparent in the shape of the tides every day, which change the sea water in the pool and bring in new organisms from the open ocean (as well as allowing others to escape back into the sea). The tides also change the physical characteristics of the pool and its surroundings. When the tide is out, the rock pool is a collection of organisms living together in a fairly clearly defined place. When the tide is in, the pool may become no more than a small depression on the rocky sea bed. Now let’s look at the components of our rock pool ecosystem. Remember, any ecosystem contains living things, a physical environment and a source of energy. The most obvious living things will tend to be the largest ones: seaweeds, sea anemones, whelks, shrimps, fish and so on. But this shouldn’t blind us to the importance of the organisms we can’t see. For example, the water itself is full of tiny plants and animals – called ‘plankton’ – that are food for many of the larger creatures. And the water and rocks contain huge numbers of the simple single-celled organisms called bacteria, and other microscopic forms of life, that play an important part in the working of the ecosystem. The most obvious components of the physical environment of the pool are the rock that surrounds it, the sea water in it, and the air above it (when the tide is out). But these physical factors are far from fixed. The tides, and the effect of sunlight on the exposed pool, mean that the organisms that live in it must be able to withstand changes and extremes of, for example, temperature or salt content. Some small pools dry up altogether in the summer or ice over in winter when the tide is out. Almost all of the energy that supports the life in the pool arrives in the form of light from the sun. Some of this energy is captured by seaweeds attached to the rocks and microscopic plants (types of plankton). These plants are eaten by animals, which are eaten by other animals, and so on. But the sun is not the only source of energy involved in the workings of this particular ecosystem: the tides that sweep across the pool are driven up and down the beach by the gravitational pull of the moon. Activity 1 Using your knowledge of rock pools, pick out a few of the key features of the ecosystem, using these headings: rock pool ecosystem – links to other ecosystems and the wider world ecosystem living things physical environment energy. Make some note on the key features, in the box below. Here is a list of key features for each heading: rock pool ecosystem – links to other ecosystems and wider world ecosystem – living organisms, physical environment, energy living things – plants, animals, plankton, bacteria physical environment – rock, sea water, air, tides energy – sunlight (also tides caused by pull of the moon). Did you note many of the same points? Is there anything else you’d include? Is there anything you’d leave out? Remember that it is the observer – you or I – who defines an ecosystem, and selects which organisms or aspects of the environment to study. In much the same way, you have to decide what is important when you make notes. However big or small our ecosystem, and whichever aspect of the system we choose to study, it is ecology that provides the framework that allows us to investigate how it works – and to wonder at the beauty and strangeness of it all. 1.3 Study a habitat It is possible to observe ecosystems physically, mapping out observations to determine the network that exists in a given habitat. These observations provide a valuable baseline for understanding a given ecosystem, making it easier to determine the possible negative factors that might be influencing it. In this video, we join a group of students who are learning how to classify habitats, in the field. After you watch the video, add a definition of an ‘indicator species’ to your glossary. Study a habitat SPEAKER 1 What the students are doing at the moment is learning how to do a phase one habitat survey. They're trying to summarise their observations on a very coarse scale using a map. SPEAKER 2 There's a complete description in here of what you're supposed to do, how you're supposed to do it, how you're supposed to undertake your fieldwork, how you're supposed to prepare your final maps. SPEAKER 1 They have to look at the different types of vegetation and classify them into broad groups like grassland, woodland, scrub, fen, bog, mire, fairly broad categories. And then, by looking at the plants, it enables them to decide which one of those categories the vegetation falls into. And we have a colour coding scheme that they have to learn from a reference book with very clearly defined nationally agreed colour codes. And then they can further map and shade it in, depending on which habitat they're looking at. SPEAKER 2 So you have these coloured maps produced. And the idea is those colours are uniform, if you like. So it uses the same colours for the same type of vegetation anywhere in the country. And generally, it's sort of green for woodlands, orange is for grasslands, purple is for mires.And if you identify a piece of land as being, for instance,-- what should we choose? Marsh or marshy grassland? We've got to decide what type of grasslands. And it could be an acid grassland, a neutral grassland, a calcareous grassland. It could be improved grassland. There's a range of possibilities. As an example, see the fields which are a much sort of richer green colour? Those are fields which have been improved, and you can improve fields by adding lots of fertiliser to it. Or you can sometimes sort of partially improve land by having a very high stocking rate. This stuff we're on here, would you classify this as being improved or semi-improved? Do you think there's any chemical fertilisers put onto it? Any sort of huge stocking rate, lots of sheep dung and stuff? OK. So we've got a piece of grass which is probably unimproved. And what we're looking for are indicator species which sort of help us make that decision. You've already seen the mat grass. Remember the map grass with the tillers? So lots of tillers there. So there's masses of mat-grass here. So we've got quite a few plants here which are all indicating acid conditions. So we can classify this area then as being an acid grassland. SPEAKER 1 It's enabled us to take a big picture. Mapping exercises like this have been going on for the last 15 years or so, and we've been trying to cover the whole country. SPEAKER 2 Don't worry now about everybody trying to mark down everything. We'll run through it partially together when we get back in. So have a look at the map and maybe make a few notes on it.Almost all of the area between where we are now and the eastern boundary-- and the eastern boundary is that long sloping line which follows the track coming up from the road that eventually heads to the centre-- all of that is going to be mapped as being unimproved acid grassland. SPEAKER 1 It helps us to identify areas where you are likely to find certain rare species. So we can decide on areas that need protecting. Where you have areas of development it helps you to decide on whether a developer should go ahead, what kind of development should go ahead, and any mitigation factors you might have to bring in, any habitat creation you could do while you're doing it. SPEAKER 3 It all came together when I climbed to the top of that hill because you're sort of looking at areas on the ground and start looking at what vegetation there is and trying to identify the underlying geology by what size or what plants there are. And when you actually go up there and have a look, it actually makes it quite apparent the different patches, brighter green areas of the grasslands and the fen areas are obviously a different colour. So it sort of brings it all together. [MUSIC PLAYING] 1.4 The wetlands of Wicken Fen The wetlands of Wicken Fen [MUSIC PLAYING] NARRATOR The wetlands of Wicken Fen-- Britain's oldest nature reserve. Some 7,000 different species of mammals, birds, plants, insects, and other invertebrates have been recorded here, making this one of the most biologically diverse places in the UK. Why is Wicken Fen so rich in species? What is the relationship between habitat diversity and species diversity? And what role does conservation play in promoting biodiversity at this very special reserve? Wicken Fen, this is one of the last surviving fens in Western Europe. For much of the year, this low-lying land is waterlogged, creating the unique fen environment of waterways, marshes, meadows, and woodland. [MUSIC PLAYING] A remnant of the great fen that once covered six and a half thousand square kilometres, Wicken Fen is situated in Eastern England, just below The Wash in the county of Cambridgeshire. Today, 99.9% of what was the great fen has been replaced by farmland, and Woodwalton, Holme, Chippenham, and Wicken are the only remaining areas of fen. Wicken Fen, though it covers less than 4 squarer kilometres, is now the largest fen in the region. A nature reserve for just over 100 years, the fen is home to a tremendous diversity of species. Near the woods, a herd of deer, one of the fen's 29 mammal species, graze the scrub. Among the grasses and wildflowers of the fen meadows, Ringlet butterflies flutter, one of a thousand species of butterflies and moth recorded here. There are 200 species of bird on the fen, including reed warbler. Counting all of the different species of Wicken Fen, including animals, plants, and fungi, is one way of determining its level of biodiversity. JOANNA FREELAND Biodiversity is a contraction of the terms biological and diversity, and it basically just refers to the number of species and the number of individuals within each species, living within a particular place and a particular time. The easiest way to measure biodiversity is just to go out and count, first of all, how many species there are and second, how many individuals there are within each species. NARRATOR But biodiversity is more complex than just a headcount. It's influenced by a number of factors. One of these is the range of habitats within an area. A habitat is an environment in which a species, be it plant or animal, can live. JOANNA FREELAND Within the UK, Wicken Fen would definitely be considered to be a biodiversity hotspot. There's an estimated 7,000 species of insects, plants, mammals, all other different types of taxa at Wicken Fen. And of course, going along with that, there's a huge range of different types of habitats. NARRATOR The open water is just one of many habitats at Wicken, each with its own characteristic species. Because Wicken is a fen, its multiplicity of habitats depends in part on moisture levels. The wettest areas are the waterways, ditches, and ponds. These contain aquatic plant species like water lilies and pond weeds.Adjacent to these areas are shallow waters which are suitable for reeds. In areas where these waters dry in summer, fields of sedge dominate. Dryer again are the fen meadows, which are home to wildflowers and grasses. Dryer areas may also be covered by woodland and bushes, like birch and gelder rose. In terms of biodiversity, habitat and species are closely linked to each other. JOANNA FREELAND The more habitats that you have within an area, the more species, as a rule, you will find within that area. That is because, for the first part, habitats are defined, to a fairly large extent, by the species living within them. Wicken Fen is a conservation area in the east of England, near Cambridge. It is one of Britain’s oldest nature reserves and home to around 7,000 species of mammals, birds, plants, insects and other invertebrates. Wicken Fen has been described as ‘biodiversity hotspot’, and offers the opportunity to observe multiple habitats, each with its own ecosystem, interacting with each other and forming larger ecosystems. The wide range of habitats, the diversity of species, and the complex food webs present in Wicken Fen are all factors in determining biodiversity. Take this opportunity to explore the area around Wicken Fen. 1.4.1 Following the food web in Wicken Fen Following the Food Web in Wicken Fen NARRATOR The sedge-field habitat is made up of many different species. The saw-sedge predominates but other plants also thrive. These include marsh bedstraw and bindweed. Invertebrate species found here include snails and beetles. ADRIAN CALSTON Wicken is so rich in biodiversity today because it has such a range of habitats from the scrub through to the sedge fields, the reeds, and all these ditches that run across. So there's a lot of different habitats and they can all support different species. NARRATOR This can be clearly seen by comparing the species of two neighbouring fen habitats-- a fen meadow and woodland. The meadow is filled with grass and wildflower species. There's the marsh pea, for instance and thistles. These plants are home to a wide variety of invertebrate species. ADRIAN CALSTON Got a variety of very, very small little flies in here, several different varieties of spider. That little tiny one running across is a money spider. There's one generically known as a garden spider there. And there's a caterpillar. Two different species there. And one or two hoverflies and a lacewing. NARRATOR The woodland habitat beside the meadow includes tree and shrub species like hawthorn. This habitat is suitable for a different group of invertebrates. ADRIAN CALSTON We're now in the area of scrub about 20 yards from the meadow we've just come from. And in here there are different species. As you can see, they're very, very small. There's a different species of spider there, another one there, another one there, another one there, five or six different species. What we can see here is that we've got quite a few different species from the ones that we found in the meadow. And it shows that with a lot of species, particularly insects, they're very dependent on the specific type of habitat. So we've got two different habitats really quite close together containing different species. And as a result of that, we can see that a site which has got a variety of different habitats is going to have a much higher biodiversity than a site with just a single habitat. NARRATOR Biodiversity doesn't simply depend on the range of habitats. It's also influenced by the way species interact with one another. This is the Lode, the main water channel running through Wicken Fen. One way its plants and animals interact is through the food web. Each species is food for other species. The more species there are to eat, the more there will be eating them. The food web underpins biodiversity because it means many different organisms can coexist.At the base of a food web are plants. The slow-flowing clear waters of the Lode offer the perfect growing conditions for submerged aquatic plants. Plants use energy from the sun to create new tissue through photosynthesis. JOANNA FREELAND When there is plant tissue available, then there is food for herbivores, which are organisms that eat plants. When plants die, they provide food for detritivores, which are small organisms, often microorganisms, that eat dead and decaying material. And of course, when the herbivores die, they in turn provide more food for detritivores. And herbivores also provide food for carnivores, which are animals and occasionally plants that feed on animal tissue. NARRATOR In the Lode waters, herbivores like water snails nibble the aquatic vegetation. Small carnivorous fish, including roach and minnows, are prey for larger, freshwater carnivores like pike. While some of these species spend their entire lives under water, others may move between habitats at different stages of their development and so become part of different food webs. Dragonflies and damselflies, for instance, spend much of their life under water as larvae and emerge from the water when they mature. In the process, they're part of two food webs-- the aquatic and the terrestrial. Rory McKenzie-Dodds is from the Dragonfly Project and regularly visits the Fen to observe the 20 species of dragonfly and damselfly found here. RORY MCKENZIE-DODDS Can we go nearer this bank on port side? Dragonflies are particularly interesting from the point of view of food webs. Underwater dragonflies will be eating midge larvae and mosquito larvae. At this larval stage they tend to get eaten by insectivorous fish. NARRATOR Underwater the larvae are carnivorous. This one is pursuing a water snail. But at the same time they are food for other carnivores. In this case a carnivorous insect, the water boatman, is feeding on a damselfly larva. Within the aquatic food web, the larvae are both predator and prey. RORY MCKENZIE-DODDS Probably the most dangerous time is the moment when they actually climb out of the water and then they start to pump their wings out. And really they can't move at that stage and they're ideal meals for, particularly, birds. Blackbirds make a great habit of munching them, so do wagtails. In the adult stage they continue to be carnivorous. They eat midges and gnats and mosquitoes, butterflies, bees, very often each other. That's what they eat. And they're eaten in turn by birds. Hobbies, for example, make a particular speciality of catching dragonflies. NARRATOR Now part of the terrestrial food web, adult damselflies and dragonflies are also prey for a diversity of carnivores including spiders, wasps, frogs, and small mammals. This example demonstrates how complex food webs support many species within the habitat. So the range of habitats, the diversity of species, and the complicated way in which parts of the food web interact, are all factors in determining biodiversity. The definition of an ecosystem can be framed in terms of energy flow. You need to know what organisms are living in it – the biodiversity of the system. Next, you can work out how the organisms are linked. The sum of the nutritional links between organisms in an ecosystem is known as the food web. Activity 2 There are two food webs mentioned in the film and one animal that links them together. What is the significance of this link? Note your thoughts in the box provided. The dragonflies link the aquatic with the terrestrial food webs. Energy obtained by the dragonfly larvae feeding below the surface is transferred to the terrestrial food chain. This example emphasises the complexity of links that need to be unravelled if a picture of energy flow is to be drawn accurately. 1.4.2 Managing habitats in Wicken Fen The diversity of life in Wicken Fen is influenced by the way in which humans use the habitats that make up the ecosystem, as Professor Gowing explains. It is possible to determine the best management programme, by setting up an experiment. Whilst watching the video, consider the following: Why does Wicken Fen have to be managed? What were the key features of the experiment that was set up at Wicken Fen in the 1920s? Go to the Week 1 forum to discuss your thoughts with fellow learners. Open this in a new tab and come back here when you're done. As learners can study at their own pace we cannot always guarantee there will be other active learners while you are studying. Managing Habitats in Wicken Fen NARRATOR Key to the maintenance of this diversity is the management of habitats, a human intervention that has been happening for centuries. At the edge of the fen, the Cottage Museum depicts how life may have been for workers on the fen before it became a nature reserve. The vegetation was cut for thatching local houses, and as bedding and feed for domestic animals. Tools such as this were used to cut peat for fuel. The result is a landscape stamped with centuries of rural culture-- physically, in the peat diggings, paths, ditches, and dykes, and ecologically, in the plant and animal communities that have developed over time. JOANNA FREELAND The reason why Wicken Fen has to be managed is because humans have been cutting it back, and tending the ditches, and so on, and creating, as a result of this, certain habitats. And within these habitats, different sets of species co-exist with each other. NARRATOR Wicken Fen was given to the National Trust in 1900, since when it's been run as a nature reserve. Tasks, such as hay cutting, used be part of people's livelihood. Today, they are continued as a means of conservation. The driving force behind much of the Trust's activity is managing a natural process known as succession. JOANNA FREELAND Succession is the natural way in which habitats change over time. If you start with a habitat that has essentially nothing living there, the first species that come in will be weedy plant species, because they can survive on soil that has low nutrients. And they can take energy from the sun, and therefore, form the basis for a food web to begin there. Associated with these plants-- these first plants coming in-- will be a range of invertebrates. And when the plants and the invertebrates die, the detritivores will help to decompose them. Their nutrients will be released into the soil. And as the soil becomes richer, a wider range of plant species can now come in and grow there. And over time, you'll get the progression from weeds to grassy species to shrubs, hedges. And eventually, you'll end up with forests there. NARRATOR If woodland were the only habitat here, then biodiversity would plummet. And if succession were allowed to proceed naturally, much of the fen would be covered by bushes or trees. It's only by halting the process of succession, at various stages, that so many habitats can be maintained. This idea of conserving habitats by managing succession was first explored in the early 1900s. Wicken was one of the first sites at which the effects of management on habitat diversity were explored. An early exponent of this was Harry Godwin, a pioneer of plant ecology. ADRIAN CALSTON These are the Godwin plots. And they're an experiment that was set up in the 1920s to look at the impact of management on vegetation. There are four plots. And then, down at the far end, there is a control. And the idea is to see what happens with different frequency of cutting, and the impact of that on vegetation. And what we've found out, also since then, is that obviously has an impact, also, on the types of animals that live here as well. So where we are now, we are in the first year. And this vegetation is cut every year. And it's dominated by grasses. And this is the purple moor grass. In addition to grass being in here, we can see that there are a number of flowering plants. This one here is purple loosestrife. And in this kind of community, we'll find that there are butterflies, such as the large skipper and the small skipper, and moths, such as the silver bard, which occur. And if we just move a couple of yards over to here, we're now in the area that's cut every two years. And here, a new plant has come in. This one here is called the saw-sedge. It has a very jagged edge along the back of it. NARRATOR Even as little as one year difference between cutting periods has a significant impact on the species that are able to grow. This difference can be attributed to succession. ADRIAN CALSTON Well, I'm now moving from the area which is cut every two years into this one, which is cut every three years. And immediately, you can see that this is much denser and much taller than the previous area. It's almost dominated, now, by the saw-sedge. But we can begin to see, now, the beginnings of seedlings of small shrubs. This one here is alder buckthorn, for example. Then, moving along over here, we can see the reed is quite dominant. And this one, obviously, is a couple of years old, as it's got a dead flower head on the top. Not only is the vegetation different with this longer cutting regime, but this is also reflected within the animals. Now some animals live as little, tiny larvae, for two or three years, within side the stems of these grasses. And of course, in the plots over there where they're cut every year, those animals have got no chance of maturing and becoming adult, whereas here, they actually can. And one animal that lives in here is a moth called the reed leopard. It lives as a larvae, inside here, for two to three years, and then emerges as the adult. And here, it's able to do that. What you can also see within this plot, as well, is there are an awful lot of spiders webs. As there's no annual disturbance, these animals can build these complicated webs, and then hunt around, in this longer grass, upon the things that also live within here. This is the compartment that's cut every four years. And again, we can see very tall, very coarse vegetation dominated by the reeds and the sedge, but also, increasingly now, by areas of scrub. Here-- this plant here is a creeping willow, a little bush that's beginning to come in. It's coming in because it's been cut so infrequently it's able to shoot and actually get growing, and grow reasonably tall. And then finally, moving on over to here, this is the area which is not cut at all. And we can see, now, it's dominated by bushes, which are growing quite tall now. This plant here is the gelder rose. Over there is privet, which is now coming into flower. And above us is a birch tree. NARRATOR The trees and bushes of the control plot, which hasn't been cut at all, represent the final stage of succession in this area. The plots illustrate the process of succession from an open meadow to woodland. The different stages are entirely a result of how frequently each plot is cut. ADRIAN CALSTON The Godwin plots at Wicken show a number of different things, really. They show the role of management-- that if you manage things in one type of way, you can create one type of habitat. If you manage it differently, a different habitat can be created. But what they also show, if you look at them all in sequence, it shows you a succession from, basically, fen meadows through to scrub. 1.5 Week 1 quiz This quiz is about defining the term ecosystem and applying your knowledge to a simple ecosystem. Complete the Week 1 quiz now. Open the quiz in a new window or tab then come back here when you're done. 1.6 Summary of Week 1 In the final video of this week, Dr David Robinson, Senior Lecturer in Biological Science at The Open University, discusses what you have learned so far in this course and then introduces some of the ideas and examples explored in Week 2. Interactions DR. MICHAEL GILLMAN There are two main ways of defining what we mean by an ecosystem. Some people talk of organisms that share similar conditions. But a more useful definition is to talk about how organisms interact, how they work as a system. This is what Arthur Townsley had in mind when he coined the phrase. So ecosystems are all about interactions. And if we're going to get to grips with ecosystems, we've got to get to grips with those different interactions. But hang on, there's billions and billions of different interactions between millions of different species. Now obviously, we're not going to be able to analyse every single last one of those, but what we can do is look at the different types of interactions. Luckily, there's not so many of those. It's all about energy and nutrients. The ultimate energy source is the sun, and most plants interact with it using photosynthesis to turn the sun's energy into their own chemical energy. That energy is then passed on through a range of different feeding interactions. One way to classify all the different types of interactions is according to whether organisms have a net gain or a net loss from any interaction, whether they win or lose. Any win or loss of nutrients or energy may be vital. Winning or losing can affect whether any one organism survives or dies. There are six possible outcomes that are observed in natural systems. Commensalism, in which one species gains and there is no effect on the other species. Mutualism, in which both species gain. Parasitism, predation, and herbivory, where one species loses and one gains. And competition, where both species lose, or both individuals within a species lose. Analysing interactions like this helps us to understand what's going on in the ecosystem. It can also help us define an ecosystem's boundaries, which aren't always as clear-cut as you might think. DR. VINCENT GAUCI You could have a very simple ecosystem that has an apparent boundary in a pond or a lake. But the situation then gets more complicated because you then have runoff from the surrounding hills, and that brings nutrients into the lake. And so, it's not quite as easy as you think it might be. DR. MICHAEL GILLMAN So interactions help us to define the boundaries of an ecosystem. But in order to understand the functioning, we need much more detailed information. We need to know about energy. We need to know about the rate of transfer, we need to know about the route of transfer, and we need to know about the efficiency of transfer. And that brings us back to the primary source of energy, the sun. DR. VINCENT GAUCI We have a waveform of energy coming through the atmosphere from the sun and light, and that gets converted to a chemical form of energy. Now that chemical form of energy uses carbon, so you're making sugars and starches. Of all the sunlight that comes into the Earth's atmosphere, about 8% is trapped by green plants through photosynthesis, and we call that gross primary productivity. Now, of that 8%, about 50% is immediately respired out, so the carbon that's been fixed then leaves the plant, the remaining 50% goes into building the plant tissues. That can be leaves and stems. But also into leaving a little extra for a bad day, winter time. There'll be some that'll be stored away in roots and rhizomes, and a little bit will also go into reproduction. So, the manufacture of seeds. DR. MICHAEL GILLMAN There are four ways in which the plant's energy can be passed on within the ecosystem. It could be stored as perennial biomass. It can pass as dead tissue to decomposers. It can get eaten with its energy passing on to herbivores. Or it could be passed on through what's called soluble losses. DR. VINCENT GAUCI Some of this carbon that has gone into the plant then leaks out through its roots. This form of carbon could be considered a loss from the plant, but actually the plant is investing in a process that actually assists it. DR. MICHAEL GILLMAN It may be a loss to the individual plant, but it can be thought of as an investment in the whole ecosystem, a kind of plant tax if you like, and it can make a huge difference. DR. VINCENT GAUCI If you consider trees and forests, they develop these interactions with what we call mycorrhizae. Now these mycorrhizae do something that the plant can't. They're particularly good at taking nutrients out of the soil. In giving those nutrients to the plant, in return, they will get a source of carbohydrate or sugar, which sustains them. About a quarter or carbon loss from the plant goes into this mycorrhizae, and this interaction is actually responsible for a huge amount of what we call soil respiration; that is the CO2 that is lost from the forest floor. So it's tremendously important in terms of the cycling of carbon in an ecosystem. DR. MICHAEL GILLMAN It's not always a win-win scenario. Some net production is simply lost, washed away, or leached out. No system is perfectly efficient, and ecosystems are no different. Some are more efficient than others. Understanding the types of interactions and the flow of energy and nutrients is vital to understanding how ecosystems work. There are different ways that an ecosystem can be defined and you discussed this with other learners, to reach a working definition of an ecosystem. You examined the core concept of an ecosystem through the example of a rock pool. Guidance as to how to study ecosystems was provided through the case study of Wicken Fen. The next part of our learning journey starts with carbon and the capture of energy from light by plants. Plants are at the base of the food chain for all the animals in an ecosystem. The familiar woodland is an ideal place to begin to understand ecosystems in more depth. If you would like a short break or to find out more about coastal habitats and Wicken Fen visit our Ecosystems area on OpenLearn. You can now go to Week 2. Week 2: Understanding ecosystems Introduction Ecosystems comprise more than relationships between organisms in the habitat. They are affected by factors such as light, water, carbon dioxide and nutrients and, of course, human activity. It is nearly impossible to understand all the interactions occurring in a given ecosystem at any one time, but it is possible to observe the types of interactions that are present – and there are six, described by Dr Mike Gillman in the following video. Analysing interactions in terms of these types can help to define the boundaries of a system, though this is not an easy task. Dr Vincent Gauci considers the routes of energy loss in ecosystems. Interactions DR. MICHAEL GILLMAN There are two main ways of defining what we mean by an ecosystem. Some people talk of organisms that share similar conditions. But a more useful definition is to talk about how organisms interact, how they work as a system. This is what Arthur Townsley had in mind when he coined the phrase. So ecosystems are all about interactions. And if we're going to get to grips with ecosystems, we've got to get to grips with those different interactions. But hang on, there's billions and billions of different interactions between millions of different species. Now obviously, we're not going to be able to analyse every single last one of those, but what we can do is look at the different types of interactions. Luckily, there's not so many of those. It's all about energy and nutrients. The ultimate energy source is the sun, and most plants interact with it using photosynthesis to turn the sun's energy into their own chemical energy. That energy is then passed on through a range of different feeding interactions. One way to classify all the different types of interactions is according to whether organisms have a net gain or a net loss from any interaction, whether they win or lose. Any win or loss of nutrients or energy may be vital. Winning or losing can affect whether any one organism survives or dies. There are six possible outcomes that are observed in natural systems. Commensalism, in which one species gains and there is no effect on the other species. Mutualism, in which both species gain. Parasitism, predation, and herbivory, where one species loses and one gains. And competition, where both species lose, or both individuals within a species lose. Analysing interactions like this helps us to understand what's going on in the ecosystem. It can also help us define an ecosystem's boundaries, which aren't always as clear-cut as you might think. DR. VINCENT GAUCI You could have a very simple ecosystem that has an apparent boundary in a pond or a lake. But the situation then gets more complicated because you then have runoff from the surrounding hills, and that brings nutrients into the lake. And so, it's not quite as easy as you think it might be. DR. MICHAEL GILLMAN So interactions help us to define the boundaries of an ecosystem. But in order to understand the functioning, we need much more detailed information. We need to know about energy. We need to know about the rate of transfer, we need to know about the route of transfer, and we need to know about the efficiency of transfer. And that brings us back to the primary source of energy, the sun. DR. VINCENT GAUCI We have a waveform of energy coming through the atmosphere from the sun and light, and that gets converted to a chemical form of energy. Now that chemical form of energy uses carbon, so you're making sugars and starches. Of all the sunlight that comes into the Earth's atmosphere, about 8% is trapped by green plants through photosynthesis, and we call that gross primary productivity. Now, of that 8%, about 50% is immediately respired out, so the carbon that's been fixed then leaves the plant, the remaining 50% goes into building the plant tissues. That can be leaves and stems. But also into leaving a little extra for a bad day, winter time. There'll be some that'll be stored away in roots and rhizomes, and a little bit will also go into reproduction. So, the manufacture of seeds. DR. MICHAEL GILLMAN There are four ways in which the plant's energy can be passed on within the ecosystem. It could be stored as perennial biomass. It can pass as dead tissue to decomposers. It can get eaten with its energy passing on to herbivores. Or it could be passed on through what's called soluble losses. DR. VINCENT GAUCI Some of this carbon that has gone into the plant then leaks out through its roots. This form of carbon could be considered a loss from the plant, but actually the plant is investing in a process that actually assists it. DR. MICHAEL GILLMAN It may be a loss to the individual plant, but it can be thought of as an investment in the whole ecosystem, a kind of plant tax if you like, and it can make a huge difference. DR. VINCENT GAUCI If you consider trees and forests, they develop these interactions with what we call mycorrhizae. Now these mycorrhizae do something that the plant can't. They're particularly good at taking nutrients out of the soil. In giving those nutrients to the plant, in return, they will get a source of carbohydrate or sugar, which sustains them. About a quarter or carbon loss from the plant goes into this mycorrhizae, and this interaction is actually responsible for a huge amount of what we call soil respiration; that is the CO2 that is lost from the forest floor. So it's tremendously important in terms of the cycling of carbon in an ecosystem. DR. MICHAEL GILLMAN It's not always a win-win scenario. Some net production is simply lost, washed away, or leached out. No system is perfectly efficient, and ecosystems are no different. Some are more efficient than others. Understanding the types of interactions and the flow of energy and nutrients is vital to understanding how ecosystems work. 2.1 The carbon cycle Dr Vince Gauci describes how carbon that plants have fixed from the atmosphere moves through an ecosystem and eventually is returned to the atmosphere. Carbon can be stored for long periods in the natural environment. When you've watched the video think of some examples of places where carbon is stored. The peatbog problem DR. FRED WORRALL Our largest store of carbon in the country are not our forests, it's our peat bogs. The peat bogs of the UK store more carbon than the forests of Britain and France combined. JULIETTE MORRIS How significant a part can peat bogs play in helping to tackle global warming? DR. FRED WORRALL Oh, oh tremendous. The amount of carbon stored in our peat lands in the UK is the equivalent of 21 years of total UK CO2 output. So that's all the CO2 from cars, power stations, everything. JULIETTE MORRIS Gosh. DR. FRED WORRALL There's 21 years worth. And that's a relatively conservative estimate. So if we damage these areas, we're going to be contributing to our CO2. But also, this stuff has been growing here for thousands of years, and there's no reason why it couldn't keep growing for another 6,000, 8,000 years. This has been growing here since the last ice age, so it can keep on growing. And that means it can keep on storing carbon and keep on taking carbon out of the atmosphere. So if we manage these well, they will actually help us solve our problem. If we manage them badly, they will contribute to our problem. JULIETTE MORRIS Keeping across all these carbon movements is Fred's colleague, Bob Baxter. JULIETTE MORRIS So how does it work? DR. BOB BAXTER Well, what it's got is two major components that you can see here. One is simply just measuring. As air passes through the prongs of the system, the concentration of carbon dioxide in the atmosphere at 10 times per second. So very rapidly. And coupled with that, we have basically wind coming across the landscape, bouncing across the landscape if you like. We need to know the wind speed, so we use something called a sonic anemometer, which are the prongs that you can see on that system there. People at home may recognise the cup anemometer, which you see on weather stations often spinning around, telling wind speed. But that's just in one direction, just in the horizontal. We need to know whether the air is moving up from the land or down to the land. JULIETTE MORRIS And that then obviously tells you which direction the carbon's going in. DR. BOB BAXTER Yes, exactly. JULIETTE MORRIS Ultimately, what's going to happen to all your research? DR. BOB BAXTER So, what we're trying to do here at the present time is get a long run of information day by day. Early days at the moment in terms of what is happening certainly, but through modelling, through trying to predict into the future, then we're trying to use this as a baseline information of a number of years trying to predict what is happening in terms of global warming. DR. VINCENT GAUCI At the Open University, we're also researching greenhouse gas emissions from carbon-rich wetland ecosystems. Bob Baxter uses a micro meteorological tower to integrate over very large scales. But if you're interested in the very fine scale, like we are, all you need is this. It's called a chamber and it's used to trap emissions from the soil so we can analyse what they are. So you place a chamber on the soil's surface, and here we've got a nice soggy, peaty soil surface, which should be producing lots of methane, and you define the volume of the chamber by placing a lid onto the top there and sealing it. It's simple but effective. With the chamber in place, we can take an initial sample. This should show a composition that is similar to the ambient local atmosphere. It's our baseline sample. And then we wait, taking samples over time. 20 minutes later, I come back and take my third and final sample of the volume. I would expect to see a much larger concentration of methane in the chamber. The samples are analysed in the lab so we can calculate the rate at which methane is being produced and get an idea of what's happening to an important carbon store. This kind of field work looks at methane emissions as they are today. But in the lab, we can travel back in time and that's what Ph.D. student Carl Boardman is doing. Inside these sealed units, Carl has a selection of peat cores from a bog and a fen, two different types of peat land ecosystems that produce methane. The units are linked to gas cylinders so Carl can precisely control the makeup of the air inside. And he's particularly interested in the level of CO2. CARL BOARDMAN An experimental CO2 level is approximately half modern day concentration. And now that's significant because approximately a half modern-day concentration is equivalent to what was present 21,000 years ago, which was the last glacial maximum. So what we're trying to do is trying to recreate the CO2 concentration in the atmosphere back them. DR. VINCENT GAUCI So the air in Carl's experimental cabinet is the same mix of gases as the air would've been at the height of the last ice age, so we can find out how the availability of CO2 would've effected methane emissions back then. The way he samples and records methane emissions is similar to what I was doing out in the field, but a little more high tech. With the chamber in place, Carl can see a readout of the methane emissions immediately. CARL BOARDMAN What we're looking at now is a continuous readout of methane emissions coming from the peat core. On the X-axis, we've got time. On the Y-axis, we've got methane concentration in parts per million. The flat line before 800 seconds is the ambient methane concentration. About 800 seconds is when the chamber was put onto the peat core. When the chamber has been put onto the peat core, what you can see now is a linear increase in methane concentration with time that's coming from the peat core. The main reason why we're doing it is because current research is based upon modern day parameters; so when these studies or these models try to extrapolate and go back in time, they're actually constrained by the fact that they're using these modern day relationships. Well, hopefully, the results that we get from this experiment will constrain the models that are currently out there. DR. VINCENT GAUCI So, in a modern lab, like the one where Carl is conducting his experiments, you can really push or manipulate or constrain the system you're investigating to find out how it works. Same thing's happening with earth's climate system, where the carbon balance is being perturbed by human emissions. Now, we can really mimic these cycles and these perturbations in the laboratory, and that really helps us to find out what's going on out there in the real world. The cycle of carbon is the key to life on Earth. Plants absorb carbon as CO2 through photosynthesis, and its re-released over time through decomposition. But the balance of carbon is also important in regulating climate. So, as our climate changes, it becomes more and more important for us to understand both the balance and cycle of carbon. And that will help us to understand what will happen in the future. Life on earth is carbon based. A key feature of ecosystems is the passage of carbon through the system as part of the carbon cycle. Solar energy is captured in the leaves of plants and drives the incorporation of carbon into organic molecules. Carbon dioxide, in effect, combines with water to produce simple molecules. The process is called photosynthesis and in this video Sir David Attenborough describes it as the very basis of life. How does the availability of light, water, carbon dioxide and nutrients affect the productivity of an ecosystem? How plants make food DR. VINCENT GAUCI The fundamental material of all living things on our planet is carbon. Now this starts out as an inorganic, molecular gas in the atmosphere, carbon dioxide or CO2. So to get the carbon into an ecosystem you need the process of photosynthesis. It's a process that is unique to plants and certain micro-organisms, but it benefits almost every living thing on earth. Photosynthesis is how plants make their food, using a simple set of ingredients. Sir David Attenborough described it as the very basis of life. So let's leave it to him to explain how it works. SIR DAVID ATTENBOROUGH Air seeps into the leaves from pores on their surface. It circulates within them and reaches tiny granules that contain a green substance, chlorophyll. This is the key facilitator that uses the energy of the sun to bond carbon dioxide to hydrogen derived from water and produces carbohydrate - sugars and starches. These dissolved in sap are then carried from the leaf into the body of the plant, even during the night when the leaf factory has shut down. Come the dawn, the sun re-appears and the process starts up again. DR. VINCENT GAUCI So photosynthesis is the fundamental process driving the production of material in ecosystems. Light, water, nutrients, and CO2 are all key ingredients in driving that level of productivity. If you were to reduce any one of those key ingredients, that would result in a loss of productivity in a plant, like this tree here. Those four key ingredients, together with temperature, are known as environmental variables. Each one of them can affect photosynthesis and as they are unevenly spread through space and time, there can be dramatic differences in productivity across the globe and over different time scales. The availability of light varies throughout the day as the earth spins on its axis. At the Poles there can be almost constant daylight in the summer months, but most of the planet experiences a diurnal cycle - night and day, darkness and light. PROFESSOR DAVID GOWING Well, light is key to photosynthesis because it's the source of energy, and therefore it determines the rate of which photosynthesis can proceed. This means that productive ecosystems need to be in full sun, like a forest canopy. Beneath the canopy where light is attenuated by the canopy above it, then plants can operate at a much lower rate and take in much less carbon per unit time. Too much light can be a problem because if leaves can't access carbon dioxide quick enough to use that energy in photosynthesis, the excess energy becomes a problem for the leaf. It may even damage the photosynthetic apparatus. So this is an issue at the top of the forest canopy, where the leaves are in full sun. And plants have come up with a whole range of adaptations to cope with that, including pigments to try and absorb the excess light and photo respiration, where they actually respire the carbon they have just fixed to produce carbon dioxide to soak up that excess energy. DR. VINCENT GAUCI At the equator, light is available for twelve hours a day, all year around. That steady supply of energy, combined with high levels of rainfall, make the tropical rain forests highly productive. Temperatures are high all year, so water is available in liquid form. It doesn't get locked away as ice during the winter. In other parts of the word there is a different mix and cycle of environmental variables. In temperate regions, where the seasons are more pronounced, production takes place in spring and summer, when there's the most sunlight and the warmest temperatures. This cycle of production through the seasons can vary year by year. And we can see a record of variations in tree rings, with the wider rings showing warmer summers. In dry, arid areas of the tropics it's not light that's the issue. It's the availability of water that limits production. Perhaps the most powerful way to show how water limits production is to look at what happens when a desert gets wet. And that happens on a huge scale in the area of the Kalahari Desert known as the Okovango Delta. These remarkable images were filmed by the BBC programme "Plant Earth". As water flows into the delta, the landscape is transformed. With the water comes life. Plants can once again produce carbohydrates through photosynthesis, converting CO2 and water. What was once a barren desert is now a wildlife oasis. This is an extreme example of water limitation and the relief water can bring to a dry ecosystem. But to fully understand the effect of water on productivity, we need to understand the biochemistry of photosynthesis. PROFESSOR DAVID GOWING Water is essential for taking carbon dioxide out of the air because plants exchange water vapour for carbon dioxide when their stomata are open. And so a lack of water can really limit the amount of carbon a plant takes in. In environments where you have a real lack of water then plants have come up with alternative photosynthetic pathways to cope with the problem. A group called the C4 plants concentrate carbon dioxide by having specialist cells that take it in, store it, and pass it to photosynthetic cells which are located deeper within the leaf. And by doing that, they're supplying those specialist cells with enough carbon dioxide that they can utilise light to its full without the risk of excess light damaging the apparatus. C4 plants tend to occur in dry environments in high light, so savannahs would be the most typical natural environment for them. And plants that have evolved in that sort of savannah environment are quite often used as crop plants such as maize, and sugar cane, and sorghum. They all use the C4 photosynthetic pathway, which means they are extremely productive if supplied with light. Taking that one step further, an even more extreme adaptation is cacti and succulents that only take up carbon at night. And they store the carbon as organic acids in their big, fleshy cells, for later use during the following day where it's re-released as carbon dioxide and normal photosynthetic pathways take over. DR. VINCENT GAUCI So light and water can influence and limit productivity. The same is true of CO2, which is vital for photosynthesis. Now the concentration of CO2 doesn't vary over the planet. On a fine scale you can have concentration differences that are sufficient to affect productivity. In a dense canopy, CO2 can be used up faster than it's being replenished from the atmosphere. Manmade emissions can also have an effect. So light and water, carbon dioxide and nutrients, all directly influence the productivity of any one ecosystem. These limiting factors, together with temperature, are known as environmental variables. But that's only half of the cycle. In the next film we will look at the other half - decomposition. 2.2 Exploring oak woodland We now explore oak woodland, and the food chains and webs that exist in it. Woodlands produce a huge variety of habitats, which in turn are occupied by a huge variety of organisms. In ‘Touring an oak woodland’, Professor David Streeter introduces you to a complex ecosystem. As you watch the video, recall the concept of indicator species, which you saw in the first week and consider the follwoing questions. Why are the inter-relationships in ecosystems like woodlands so complex? What can food chains tell us about the ecosystems that exist in a particular woodland area? How have woodlands been managed? Touring an oak woodland PROFESSOR DAVID STREETER Oak woodland occupies a very special place in British natural history, because many people think that it represents the natural vegetation of much of lowland Britain before man became a significant influence. However, as no examples of that original wildwood survive, nobody really knows what it looked like. In fact, the traditional idea that the whole of lowland Britain was once covered by a continuous sea of oak woodland has now had to be quite seriously revised. Because modern pollen analysis has told us that the original woodland the predominant tree was not actually the oak but was the lime with hazel, and some elm, and of course oak as well. And what has happened is that during pre-history the lime, and to some extent the elm, has all being selectively removed. In Britain we've got two species of oak - the common or pedunculate oak, and the dumast or alternatively named sessile oak. And they have slightly different soil requirements. But in some of the sandy soils of the Weald of Sussex, like here, we have both species growing together. Historically woodlands were managed in one of two traditional ways - either as wood pasture or as coppice. Wood pasture was a method of managing woodland where tall, mature trees were allowed to grow and mixed up with grazing animals between them. Whilst coppice was a method of management whereby the trees were cut to ground level on a regular basis. And the purposes for which oak coppice was used was either for tannin, where the bark was stripped off the young shoots and the tannin was extracted from them, or as charcoal, or perhaps in some parts of the country for pit props. And what we've got here is the rather scrubby re-growth which hasn't been properly managed. On the deeper soils of the valley sides the oaks would have done much better. They would have grown into much finer specimens. So here the trees would have been allowed to mature and they would have been harvested as mature timber. Woodlands are complicated places. They occupy an enormous space from the soil to the top of the tree canopies. And that space is occupied by the trees, and the shrubs, and the herbaceous vegetation. And they generate a huge number of different kinds of habitats. And that, in turn, produces an enormous diversity of woodland organisms. Let's just have a look at some of the common woodland plants that are growing here by the edge of the path. What have we got? Well, obviously first there's bluebell. And with bluebell, what have I got down here? That's honeysuckle, and bramble or blackberry, whichever you like to call it. And bracken - the bracken fern. And if you gave that list of plants to a group of Japanese or Chinese ecologists and you said, where in the world was this list made? If they were any good they would have to say you were somewhere in Western Europe, in a woodland, on well-drained, acid soil. How would they know that? Well, firstly from the bluebell, which is one of the rarest plants in the world, because it's only found in Europe, west of the Black Forest, south of Holland and north of the Pyrenees - nowhere else. And the soil information would have come from the bracken. It only grows on acid soils and where those soils are well-drained. Honeysuckle has got a very similar distribution to the bluebell. And of course is not flowering here where I'm sitting. But behind me, where it's growing over the birches, it'll be in full bloom in a week or two's time. The tree canopies themselves support a much wider diversity of species than any other tree in Western Europe, many of them specific to the oak. And if you add to that the enormous numbers of organisms which are dependent upon dead and decaying wood, then you have the most species-rich habitat in the country. 2.2.1 Following a food chain In ‘Following a food chain’, Professor David Streeter and Professor Chris Perrins show how you can study one particular food chain in a complex ecosystem. Each individual food chain tells only part of the story of the oak woodland. What would a diagram of the food chain in the oak wood featuring the winter moth look like? Following a food chain PROFESSOR DAVID STREETER: Woods are typical ecosystems, a combination of biological communities occupying a physical environment. However, in many ways, woods are difficult ecosystems to study, because they are more complex than most. The size that they occupy is large, from the soil surface to the top of the tree canopy. And this space is occupied by trees, shrubs, herbaceous vegetation, and the ground layer, producing a huge variety of habitats, generating an enormous diversity of organisms. When trying to understand something as complex as the interrelationships between the different species in an ecosystem like a wood, it's helpful to focus on a single species in order to find out how it manages to maintain itself and survive as part of the community. NARRATOR: Many oak woods contain breeding pairs of sparrowhawks. They are the commonest woodland birds of prey. [BIRDS CHIRPING] NARRATOR: Providing food for a nest full of sparrowhawk chicks is a full-time job. PROFESSOR DAVID STREETER: Many woodland species breed in the spring, and food supplies are crucial throughout the breeding period. And they determine the success or failure of the next generation. [BIRDS CHIRPING] PROFESSOR CHRIS PERRINS: When the male is feeding the brood, it's quite noticeable. If they've got their timing right, they pretty well seem to specialise on tits. The trouble is the male tends to pluck them and pull their head off before they're brought in, so we don't have a good field guide for plucked and headless birds. And you're dependent, really, on identifying them from the legs. [BIRDS CHIRPING] NARRATOR: The tits must find enough food to raise their young. [BIRDS CHIRPING] PROFESSOR CHRIS PERRINS: We can easily fit up a camera behind the nest that's designed to take a shot each time the tit comes in with a caterpillar in its beak. You have to realise that the tits have these very large broods, and if they're to raise 10 or so young, they've got to be able to find food very easily. And the parents, actually, bring in 700 or 800 meals a day - 700 or 800 caterpillars during a day - and they can't waste time if they're to do that. [BIRDS CHIRPING] NARRATOR: Winter moth caterpillars have to find their own supply of food. Oak leaves form the final link in our food chain. How do oak trees obtain the energy and nutrients they need for growth and for making leaves? Like all green plants, oak trees use carbon dioxide and water to make vital organic compounds. This process is called photosynthesis. Photosynthesis takes place inside the oak leaves in tiny green structures called chloroplasts, which capture light energy from the sun. What happens next is a complex chain of reactions that can be summarised fairly simply. Water and carbon dioxide are converted using the sun's energy into simple sugars called carbohydrates. The oxygen released in the reaction diffuses from the leaves into the surrounding air for use by other organisms. PROFESSOR DAVID STREETER: Individual food chains tell only part of the story. Woods contain many species of animals and plants, each with their own particular food chains. And considering the wood as a whole reveals many important ecological patterns and ideas. 2.3 Fungi and the woodwide web Fungi are an important component of ecosystems, especially in forests or woodlands, as they are valuable for decomposition. Decomposition breaks down dead organic matter, releasing nutrients, which can then be reabsorbed. In this audio, Dr David Robinson talks about how fungi also have an intimate relationship with trees, which extends the woodland ecosystem underground. Reflect on the chain of interactions occurring between trees and fungi, starting with the photosynthesis in the tree canopy and ending with fungus in the tree’s roots absorbing nutrients. Investigating symbiotic relationships Investigating symbiotic relationships NARRATOR Fungi are an important part of any forest or woodland ecosystem. They are the major agents by which twigs and leaves are broken down, releasing nutrients for reabsorption by plants. And we know fungi also form a constructive partnership with living trees. David Robinson from the Open University's Life Sciences Department explains that although we have known about this partnership and relationship for some time, we are now learning more about the nature of that relationship. DR. DAVID ROBINSON You can go back nearly, I think, 400 million years and look at fossils, and you can actually determine that this relationship existed in fossils that length of time ago. So it isn't it biologically a new idea. It's only more recently that the precise nature of that relationship has been worked on. For example, it's become possible to use radioactive isotopes to track movement of molecules between fungi and tree roots. And then, even more recently, has come the applications of this knowledge, whereby horticulturalists and agriculturalists can make use of cultures of fungi to set up these relationships for themselves in areas that they're trying to plant. You can go and look at websites from people who supply mycelium - that's the fungal culture - for use in a whole range of applications. NARRATOR In Malaysia, scientists are now finding ways to apply the knowledge of the partnership between fungi and trees in order to ease a problematic relationship between economics and ecology. DR. DAVID ROBINSON I think the Interest about the Malaysian example is that they have a very particular problem that they are trying to solve there, and they're solving it with the use of fundamental research. And they're trying to pioneer techniques not only for changing logging practices in the country, but also for reclaiming areas which have been lost to forest and perhaps industrial areas of which now, with the aid of this research, they can hope to reclaim. NARRATOR In Malaysia, Dr. Lee Su See is trying to establish hardwood trees in a barren area of land using her knowledge of the way in which the relationship between fungi and trees works. DR. DAVID ROBINSON I was very struck by the experiment that Dr. Lee Su See was carrying out in reclamation. I mean, the area of land that she was working on looked absolutely impossible for plants to grow. Although, of course, there were one or two acacia plants that had managed to get established there. Of course, she was going to work on a large scale, so she couldn't just put plants there and hope for the best. She had to inoculate them with the fungus so as to get the web of mycelium and roots established. And it was obvious also that she needed to add other things, notably quite a lot of water. But it really didn't look the sort of place where you would expect to grow plants. And she clearly has had some success, and the success undoubtedly will continue. It's a long-term project, even so. NARRATOR The larger aim of Dr. Lee Su See's work is to get a sustainable source of hardwood in order to avoid the logging of untouched rain forest. In so doing, she is combining research with direct application. DR. DAVID ROBINSON So she's trying to get, really, quite large-scale production of hardwood, that is, really quite a number of trees in the same area, and get them established and growing away as quickly as possible. And this was difficult without the knowledge of the way in which the link with fungi worked. NARRATOR This growing knowledge of the large-scale web of relationships going on underground is changing scientists' views of the relationship between larger trees and saplings. 2.3.1 Unearthing the woodwide web In nature, most trees form fungal connections. The health of the forest depends on fungus – decaying branches and leaf litter are rich with nutrients, and fungi can ferry these back to living plants. Unearthing the woodwide web NARRATOR Luxurious timber in the luxuriant rain forest. Economics inextricably bound with ecology. Now, biologists are unearthing a new set of relationships fundamental to the forest. Lessons from nature could help with man-made problems and literally turn our understanding of forests upside down. The first clue can be found almost anywhere there are trees. Even in a wet Yorkshire wood. SPEAKER 1 If you come down and have a look, you can see there are cap scales. If you excavate around the fruit body, you might be able to find the remnants of a bag. NARRATOR Fungi seem unlikely candidates to start a revolution. SPEAKER 1 And you can see this membranous ring underneath. Here we have a very distinctive fruit body. It's Phallus impudicus, a stinkhorn. NARRATOR But most of the action goes on beneath the soil. This fungus is digesting a dead piece of wood. Wood decomposers are the forest's recycling service. Nothing breaks down branches better. Look carefully in the leaf litter, and there are telltale signs of other decomposers. Skeleton leaves are caused by fungi. Other leaves are bleached when fungi attack. PROFESSOR IAN ALEXANDER Fungi are important components of the decomposer system in any ecosystem and particularly so in forests. They're one of the major agents by which the leaves and twigs which fall to the forest floor are broken down and the nutrients within them released for reabsorbtion by the plants. NARRATOR In the heat and humidity of the Malaysian rain forest, this happens up to five times faster than in a British oakwood. Ian takes up the trail with forest pathologist Dr. Lee Su See. As in the British woodland, decomposers deal with death. The health of the forest depends on them. Branches and leaf litter are a treasure trove of nutrients. Fungi feed them back to living plants. Again, to get to the business end, you have to get your hands dirty. LEE SU SEE Oh, wow, look at that. PROFESSOR IAN ALEXANDER Many of the fungi that occupy this part of the forest ecosystem form these long fungal strands. So the individual fungus can colonise quite a large area of the forest floor. And this serves as a sort of plumbing system for it to conduct carbohydrates and nutrients and water. NARRATOR This is part of an extraordinary network. Not all fungi get nutrients from breaking things down. Some of them form constructive partnerships with living trees. The budding mycologists are about to log onto a "woodwide" web. SPEAKER 2 Is this it? PROFESSOR IAN ALEXANDER Yes, these are tree roots which are mycorrhizal. Some of these root tips will be infected by this fungus here. NARRATOR Mycorrhizal means the tree roots have teamed up with the fungus. PROFESSOR IAN ALEXANDER Oh, yes, look. LEE SU SEE Oh , yeah, wow. Look at that. NARRATOR And the fungus is part of a hidden underground community. It's quite interesting, the way that the mychorrhizae and the decomposers occupy the same bit of space, don't they, on the forest floor. So they must be interacting quite significantly. JONATHAN LEAKE I think below ground we have aspects of competition. But we also have a lot of interlinking between organisms. So the complexity of the below-ground linkages is something which is quite unique and different to what we see above ground, where we typically think much more about individual plants competing with each other or animals and plants interacting. NARRATOR These mycorrhizal pines have been cultivated for closer inspection. The fine threads are part of the fungus, collectively called the mycelium. JONATHAN LEAKE If you look here, you can see units that are much thicker, more robust. And these are joining together, forming an interconnected web connected back to the plant, and then extending out into the soil. At the same time, you can see there are finer mycelia extending off beyond the tips of these thicker structures. NARRATOR Plant and fungus connect in the bulbous tips. They become a single structure that looks different from either partner alone. Here, the hairs at the growing tip are replaced by mychorrhizas further up the root. It must be a mutually beneficial arrangement. In nature, most trees form fungal connections. Activity 1 Having watched the video note some answers to the following questions. What is the significance of the long strands formed underground by fungi? How do they form partnerships with trees? What do these partnerships look like? Many fungi form long fungal strands. The individual fungus can colonise quite a large area of the forest floor and this serves as a sort of plumbing system allowing it to conduct carbohydrates, nutrients and water. They form partnerships with trees through mycorrhizae which infect the tips of the tree roots. The trees are then linked into the fungal underground web. The tree roots 'team up' with the fungus. 2.3.2 Mutual benefits There is a close relationship between fungi and trees, as this video makes clear. As you watch the video note how this close relationship is being used to artificially reinvigorate ecosystems. Mutual benefits DR. LEE SU SEE Well, the dipterocarps are one of the most important family of timber trees in Malaysia and Southeast Asia. This family consists of a very large number of species, many of which have very important value as commercial timber trees. NARRATOR Behind every great dipterocarp lies a team of tiny fungi. PROFESSOR IAN ALEXANDER Underneath this big dipterocarp. Oh, yeah. Look at those. Oh yeah. The mycorrhizas are very active in competing for water and nutrients and providing benefit to the tree. In fact, the trees on these poor tropical soils just wouldn't survive without them NARRATOR So the tree taps the fungus for nutrients and water. By climbing to the top of the forest, Su See can get to the other side of the bargain. DR. LEE SU SEE Up in the canopy, the trees are photosynthesising. They're capturing the energy from the sunshine and with the carbon dioxide up here, they're going to produce sugars, which are then transported down the tree. PROFESSOR IAN ALEXANDER Down here on the forest floor is where the trees have to capture their water and their nutrients. So a proportion of the sugars, which are made up there in the canopy, come down here below ground to fuel the root system to capture nutrients. And some of that sugar finds its way out into the mycorrhizal fungus. NARRATOR With a Geiger counter and a mycorrhizal seedling, Jonathan can track the process. JONATHAN This shoot has received radioactive carbon dioxide in this box for just two hours. The shoot has photosynthesised and fixed some of that carbon. We'll check now and see where it is and where it's gone. You can hear the large amount of carbon that's being fixed by the shoots. And then, that carbon also is being transferred on to the root system. And then from the roots through the mycorrhizal root tips onto the external mycorrhizal mycelium that you can see here. NARRATOR So carbon passes not only from the shoot to the roots, but out of the plant to a totally different organism. A more sophisticated technique reveals the fungal side of the bargain. The patch contains nutrient rich leaf litter. Within weeks, the fungus will grow towards it and start to take up phosphorus and other nutrients. JONATHAN Phosphorus is one of the key nutrients in forest ecosystems that controls plant growth. And it's the one major nutrient that these mycorrhizal systems are very important in terms of acquiring from the soil. NARRATOR Adding radioactively labelled phosphorus reveals what happens next. JONATHAN JONATHAN: You can see straight away that we've got the radioactive phosphorus that we've added, some of it has already moved up. And this is where the plant is just outside of the imaging area, so it's moving up towards the plant. And if we look in a bit more detail, we can see firstly that it's moved through the fungus. This is the fungus connecting up to the plant. And then secondly, you can see that there are root tips here, mycorrhizal root tips, which have already acquired quite high concentrations of the phosphorus. This is the same system five days later. We can see the main pathways becoming even more evident now. And you could see the accumulation of phosphate, particularly in the root tips. Large amounts accumulating there. And some of it being transferred then on throughout the root system of the plant. The other part that's very exciting here is you see the distribution of phosphate that's being transferred around by the fungus. And particularly, to the growing tips where the demand is greatest as the fungus is growing. NARRATOR This all fits in to an intricate larger system. Trees and mycorrhizal fungi create a natural network with far-reaching connections. DR. LEE SU SEE Well, as you can see, the canopy consists of many layers of trees and the light filters down and the light intensity gets less and less. It gets darker as you get down to the forest floor. And when you have little seedlings down in the forest floor, most of them get very little light. NARRATOR Dipterocarp seedlings are often overshadowed by their parents. They're in very deep shade, where many kinds of tree wouldn't grow at all. In effect, they're waiting for dead men's shoes. If an older tree dies or falls, a gap in the canopy suddenly appears. Light floods in to fuel growth. Eventually, one of the seedlings will take the place of the dead tree in the canopy. But while they're waiting, the seedlings might be dependent on others. PROFESSOR IAN ALEXANDER Or when they germinate, they're going to encounter a web, a woodwide web if you like, of mycorrhizal fungi. NARRATOR As the seedlings root grows down into the soil, it releases a cocktail of chemicals. Sugars, amino acids and nutrients, an attractive meal for soil bacteria and fungi. The mycorrhizal fungus is just one of a crowd. But the plant root also releases chemicals called flavonoids. They act as a signal, and the mycorrhizal fungus is more sensitive to its message than other organisms. Under the influence of flavonoids, the fungus grows towards the root. A subtle, molecular conversation starts to take place. Closer in, a new chemical vocabulary comes into play. Cytokinins tell the fungus to branch. Now it's the turn of the fungus to release a chemical. It in turn communicates with the plant. In response, the plant switches off its natural defences and the root hairs, now redundant, disappear. The fungus has now been recognised. The stage is set for the formation of a fully fledged mycorrhizal partnership. In microcosm, this is what happens in a forest. A baby plant joins a larger one, which already has a mycorrhizal network. JONATHAN This mycorrhizal network is being supported by the larger and established plant, and the seedling growing here will become part of that network when it becomes infected and will gain the benefits of being part of that network, in terms of the uptake of nutrients. PROFESSOR IAN ALEXANDER That means that they have a ready-made system for capturing water and nutrients. And they may be getting that cheap because their parents upstairs in the sunlight up there, are producing the carbon to support this fungal web. And all these guys have to do is tap into it. NARRATOR It could be a case of parental care for a nursery full of seedlings. JONATHAN I think the big question outstanding is to what extent does this actually mean that plants no longer compete with each other in the conventional sense? To what extent are individual plants supporting perhaps individuals of other species, or even juveniles or seedlings of their own type through this network. NARRATOR If this idea is true, the seedlings are subsidised by the mycorrhizal network. The network is supported by the canopy trees. Even more controversial, something may pass from parents to offspring via the fungal web. PROFESSOR IAN ALEXANDER It's possible that some of the carbon, which comes from the over story trees and out into the web of mycorrhizal fungi, some of that may in fact find its way into these seedlings. And that means that that gives them an extra chance of surviving down here in these low light conditions until such time as a gap in the canopy opens and then, off they go. 2.3.3 Competition in forest ecosystems Discuss with other learners in the Week 2 forum the role of competition between organisms in wood and forest ecosystems. Think about the implications for competition of the fungal web. How does the shading effect of the canopy influence seedling development? 2.4 Life in trees In considering food chains in an oak wood you saw animals adapted to a life in trees. Mammals that live in trees show a range of adaptations that make them well suited to the arboreal lifestyle. Woods and forests present a number of problems for mammals that inhabit them. The habitat stretches vertically for a substantial distance yet for tree-dwellers to travel any horizontal distance they must either go down to the ground each time, or jump from sometimes flimsy branches over large gaps. Sir David Attenborough describes how squirrels have overcome the problem. Life in Trees: squirrels SIR DAVID ATTENBOROUGH Squirrels deal with the problem with dazzling ease. They're such lightweights that they can race along the thin twigs at the very far end of the branches, and they're spectacular jumpers. Their powerful hind legs provide the thrust. Their long tail acts as a rudder. And their shorter front legs serve as shock absorbers to cushion the landing. Superb sight enables them to judge distance with great accuracy, an essential ability when racing along this three dimensional highway. They're at their most acrobatic during the mating season, when males start to pursue the females. One male may begin the chase, but others quickly join in. Eventually, one wins, but as soon as he's claimed his prize, the chase will start all over again, and the female may mate with up to eight different males in a single day. But a gap this size is just too big, so a grey squirrel, like a tamandua, often has to come to the ground if it's to visit all the trees in its range. A grey squirrel can leap eight feet, but there's another tree dweller that can leap much farther than that. Although it's no bigger than my hand, it can jump from this tree to that tree over there, more than 50 feet away, an astonishing distance. But to see how it does it, we'll have to come back at night. Since they have an acute sense of smell and love seeds and nuts, maybe these will tempt one down from the treetops. They are flying squirrels. How do they fly? Just watch. Maybe gliding squirrel would be a more accurate name. They're nonetheless astonishing. That furry membrane stretching between wrist and ankle makes a most efficient aerofoil. Flying squirrels are not territorial, and as many as half a dozen can be foraging in the same area of woodland. Although this little squirrel may have travelled a very long distance in order to get this valuable source of food, it's such an expert glider, it's done so with a minimum of effort. And in forests like this one, where food sources are often very widely dispersed, the ability to travel fast and far, but with very little effort, is a very valuable ability indeed. There are few gaps in these forests that defeat them, but to cross really long distances, they do need height. They steer partly with their tail and partly by moving their outstretched legs so that they vary the tension of their gliding membrane. And you can see that they can steer when one squirrel uses the same takeoff point, but glides away to land on different trees. Even so, they're not agile enough in the air to escape birds of prey, so during the day, they sleep in holes and only emerge when it's dark. 2.4.1 The colugo An animal that is not closely related to the flying squirrel but shares common features is the colugo. The colugo is a bit of a mystery and the historical confusion is evident from its common name – the flying lemur. It neither flies (in that it doesn’t flap its limbs) nor is it a lemur. The colugo is not a monkey either, despite the fact that its main predator is the monkey-eating eagle. Having once been placed with insectivores and then with bats, it’s now in a mammalian order of its own (the Dermoptera, i.e. ‘skinwings’), recognising its ancient and distinct evolutionary beginnings. This ancient origin is why it is such an interesting animal as it early on became adapted to a tree-dwelling life. As you read about the colugo, think about adaptations that have hidden ‘costs’ to the animal. One particular evolutionary development associated with tree dwelling is taking to the air. The gliding habit evolved independently in different mammalian and reptilian lineages and yet the anatomical modifications that allow it are similar in, for example, flying squirrels and the colugo. In particular, the ‘sail of skin’, technically termed a patagium, stretches between the limbs – and a good deal further in the colugo, acting as an effective (and to some degree manoeuvrable) gliding membrane. Colugos are sizeable mammals (about the size of a domestic cat) and entirely arboreal. Their record-breaking glides (in excess of 70 m) are achieved without great loss of height. But in trees, they move about rather awkwardly. The patagium is then an encumbrance and there’s a limited ability to grasp effectively – the colugo lacks the opposable thumb of primates. So the benefits of a gliding lifestyle are achieved at a ‘cost’. The resulting vulnerability – especially to the Philippine monkey-eating eagle (a species under threat, as are colugos) – may help explain why the colugo is nocturnal. 2.4.2 Flying squirrels Flying squirrels are not closely related to the colugos but they have features in common. You have seen squirrels and read about the colugo. As you watch the video, think about how flying squirrels steer during their glides. Note the advantages of the gliding habit. The similarities between colugos and flying squirrels CHRIS PACKHAM: The best time to see them is in the first couple of hours after dark. What I'm hoping is that if I stand here and stay really quiet, I'll be in for a real treat. It's a creature I've waited all my life to see, but they move so fast. [MUSIC PLAYING] Oh, did you see that? That was amazing. Went right past my face. Flying squirrel. [MUSIC PLAYING] They really are expert gliders - they can glide for up to 200 metres. [MUSIC PLAYING] When I was a kid, I was obsessed with things that were not meant to fly - flying fish, flying frogs, flying lizards, flying squirrels - and this is the first time I've ever seen them. It was worth a 45-year wait, honestly. [MUSIC PLAYING] Ah, did you? Ah, did you see that? I felt it, it went right through my hair, seriously, centre parting. It was like having a sheet of A4 coming right at my face. And as soon as they hit the tree, they are running - and up they go. [MUSIC PLAYING] They're just crisscrossing all the trees. And they immediately scamper up to the top and then take off and glide again. And sometimes, I've noticed, they can even change direction during flight. [MUSIC PLAYING]
Ah, hit me in the chest. It doesn't come better than that, does it? Activity 2 Consider these questions and note your answers in the box below. Identify one similarity and one difference between flying squirrels and colugos. On the evidence of the video sequence, comment on how flying squirrels steer during gliding. What are the disadvantages and consequences of the gliding habit in flying squirrels? Both colugos and flying squirrels have a flap of skin stretched between their limbs on each side of the body – the patagium. However, in contrast to the squirrels, colugos are not as adept at moving through the trees as the patagium is much larger and an encumbrance except in flight. During gliding squirrels steer partly with their tail and partly be altering the tension of the patagium, which alters its aerodynamic properties. The ability to glide enables colugos and squirrels to travel long distances between trees at a low energetic cost. However, they are very vulnerable to predators and so generally only come out at night. 2.4.4 Flying foxes Many species of flying fox (fruit bat) have important roles in ecosystems, dispersing seeds, pollinating flowers or providing food for predators. As they have evolved not only have they acquired adaptations that enable them to exploit aerial and forest habitats, but they have also evolved alongside plants in a process called co-evolution. What are the likely advantages to flying foxes of their particular form of roosting, taking into account vulnerability to predators, the location of food and temperature regulation? Watching flying foxes SIR DAVID ATTENBOROUGH Gliding from branch to branch was a comparatively small step for tree living mammals, but there was one group of them that made a truly gigantic leap. Their arms changed into wings. The shoulders, the elbow, the wrist remain much the same, but the hand and the fingers changed dramatically. Flying foxes, fruit bats in Australia, they and their insect eating cousins are the only mammals that have developed true powered flight. They're so big that they can't roost in holes. Instead, they sleep out in the open, in colonies that may be hundreds of thousands strong. The thumb on each hand is free of the wing and has a hooked claw. Using that and the claws on the toes, fruit bats are surprisingly nimble, clambering about in the branches. Wings may have solved the problem of getting from one tree to another, but landing is still a challenge. As a fruit bat approaches its chosen perch, it goes into a glide. Then it lowers its toes and hooks them onto a branch. This is a textbook example of how it's supposed to be done. But some perches are more difficult to reach than others. Wings need regular grooming. They're also very delicate. But small tears quickly heal. The wing membrane is among the fastest growing of all mammalian tissues. They also fan their wings to keep themselves cool. It can be very hot hanging unprotected in the baking sun. Takeoff, too, requires a special technique. Two or three wing beats lift the body to the horizontal, and only then should the feet be unlatched. That way, you don't lose too much height. It's hard work, particularly if you're carrying a baby which is a third of your own weight. Once in the air, however, fruit bats are extremely strong flyers. They can travel great distances, as much as 30 miles, 50 kilometres, in a single night, if that's necessary to find food. They may have lost a lot of moisture hanging around in the midday sun, so their first call is often to a nearby lake, to get a drink. They do this in a rather unusual way. First, they dip their chests in the water. Then, they return to their roost and lick the moisture from their fur. But there are hazards - crocodiles. The bats only touch the water for less than a second, and usually, the crocodiles are just not quick enough to catch them. But if one miscalculates and comes down on the water, it's a different matter. They're surprisingly good swimmers. The worst danger comes when they get to land. Without being able to drop into space as they can from a perch, they find it very difficult to get airborne. Now, the crocodiles have the advantage. But a few individuals lost to crocodiles makes little impact on the bat colony. This roost alone contains a staggering five million. Living together in these vast numbers brings several important advantages. Flying foxes collect fruit and nectar of many different kinds. But knowing which species of fruit tree is in season at any particular time is not easy, and some are very unpredictable. If a few individual bats return smelling of a particular fruit, the news that this food has just come on the market spreads quickly through the whole colony. Each bat knows where trees of the various species can be found. So the next night, it'll go to its own favourite patch to collect the new fruit. That is why the whole five million don't follow one another to the same tree. Huge wings may be good for long distance flying, but they don't give great manoeuvrability in the air. And when the bats return in the dawn, hunters are awaiting them. Eagles know exactly where the bats' blind spots are and attack from below. Powerful though eagles are, fruit bats are big animals, and a hit isn't necessarily a kill. Raids like these are another reason why an individual bat finds it an advantage to roost in a colony. Since it's surrounded by tens of thousands of others, there's a good chance that an eagle will pounce on someone else. Most colonies have a resident pair of eagles that nest nearby. A breeding pair will take half a dozen or so bats a day, but that still makes little impact on bat numbers. Skilled though the eagles are in taking bats on the wing, their most successful strategy is to snatch them as they hang on the branches. Colonies of flying foxes may comprise as many as a few million individuals (five million is David Attenborough’s estimate), each with a wingspan of about 1.4 m, with the entire ‘camp’ perched on often denuded trees and engaged in intense social activity. It’s little wonder that witnessing such a site has been described as a ‘memorable auditory and olfactory experience’. Such concentrations of flying foxes are ‘visible, audible and smellable for miles’ and therefore inevitably attract predators. But congregations of this type may decrease the likelihood of any one individual falling prey to predators, such as eagles. Communication between members of the camp may also increase the efficiency of locating suitable food. But the fact that food sources are depleted so comprehensively when visited en masse raises questions as to the degree of benefit of group living. Another possible benefit of roosting is that foliage might be protective, shading these mammals from wind, rain and sun, though trees that become camps lose many of their leaves. Fruit bats, for instance, regulate their body temperature, partly by behavioural means. Huddling together in groups should in theory reduce the rate of heat loss in cooler conditions, and decrease the rate of warming when it’s very hot. In both circumstances, the surface area that each individual exposes is lessened by contact. As you saw in the video, eagles (and owls) take a toll of flying foxes in transit, and the largely nocturnal habit of these species once again probably reflects selection pressure of this type. Flying foxes living on islands (more than 60 per cent of species do so) tend to venture forth in the daylight and in such environments predators are often less evident. Flying foxes can devastate crops, but they can also maintain ‘the fertility of the rain forest’. Flying foxes can certainly help disperse trees by transporting their seeds to new locations, either through their messy eating of fruits or by seeds passing intact through the gut. The seeds of the commercially important West African iroko tree depend on the straw-coloured flying fox for their dispersal. Flying foxes also help in the recolonisation of deforested areas and in the establishment of plants on land newly formed or recently devastated by volcanic eruption. Flying foxes are also important pollinators; many island species occupy the ecological niches taken over elsewhere by insects or humming-birds, for example. The transfer of pollen from one flower to another on a different tree (i.e. cross-pollination) can confer a significant advantage to the species because it promotes genetic diversity of the next generation. So the development of mechanisms that promote cross-pollination are very advantageous to trees. In Australia, pollination of some eucalyptus species depends almost entirely on visits from flying foxes. The flowering process of the Kajeng Jaler tree from Malaysia is intimately geared to the feeding habits of the dawn bat. Its flowers open just two hours or so after dusk and drop before dawn, coincident with the bat’s feeding time. The size and shape of the flower opening ensure that only the dawn bat can enter; as its long tongue reaches down to access the nectar, the position of the pollen-producing parts of the flower (the stamens) is such that pollen is deposited on the animal’s fur. This is a further demonstration of the way in which the evolution of one species can increase its dependence on another, often reflecting some form of mutual advantage. This phenomenon is known as coevolution. 2.5 Week 2 quiz This test is about energy sources, the flow of energy through a terrestrial ecosystem and the relationships between organisms within that ecosystem. Complete the Week 2 quiz now. 2.6 Summary of Week 2 In this look back at the week, Dr David Robinson from The Open University discusses what you have learned so far in this course. The next week focuses on the adaptations of animals to the challenges posed by different types of ecosystems. Summary of week 2 NARRATOR Ecosystems comprise more than habitat, inhabitants, and relationships between organisms, and learning about ecosystems in oak woodland demonstrates how complex ecosystems can be. DR. DAVID ROBINSON In woodlands like this, we can see parts of the ecosystem, but there are intricate and complex relationships between the organisms here - far more than we initially see when we walk into the woods. There's layer upon layer of interrelationships between the organisms. For example, like the woodwide web that links the trees here with the fungi under the ground. Understanding ecosystems transforms our view of the natural world, and it makes our own relationship with the natural world much more meaningful. In the next part of our learning journey, we'll be looking at ecosystems in different parts of the world, and in particular, how some organisms survive in extreme conditions through physiological adaptations. Understanding physiological adaptations is part of the process of making sense of ecosystems. NARRATOR The learning material in this section explores physiological adaptations like evaporators in the desert and adaptations to fluctuating food supply in the Arctic. In this video, Professor Paul Tett investigates how phytoplankton travel and survive in the sea. PAUL TETT The problem for phytoplankton is that they can very rarely get light and nutrients at the same time, because light is at the surface of the sea, and the nutrients are found deep down where organic matter decays in this cold quarter at the bottom of the sea. NARRATOR Here, Professor Mimi Koehl demonstrates how some suspension feeders eat. MIMI KOEHL 3/4 of the Earth's surface is covered with water, and that water is full of particles, and a vast array of different kinds of creatures make their living by filtering those particles out of the water. Some of them, like anchovies and whales, swim around and let the water move through their filters as they go. Other animals, like sea fans and feather duster worms and feather stars sit on the bottom and put their filters up in the current. NARRATOR In this audio, Professor Aaron Bernstein describes some of the wonders of the microbial world and how it redefines our understanding of life. AARON BERNSTEIN The diversity of genes in the microbial world - we know that that is far greater than the diversity of genes in the rest of the living world. But really, we're utterly ignorant about the microbial world. In fact, it is the last great unexplored frontier. Woodlands are a good example of an intricate and complex ecosystem and you have now seen that there is a fascinating web of relationships beneath the ground that forms the wood-wide web. Above the ground there are animals that are well adapted to glide through the trees and you explored the comparisons between the adaptations of squirrels, colugos and bats. Next week we’ll be looking at ecosystems in different parts of the world, and in particular, how some organisms survive in extreme conditions through physiological adaptations. Understanding physiological adaptations is part of the process of making sense of ecosystems. Examples will be taken from extreme habitats – deserts and the polar regions. If you would like a short break, or to find out more about studying with The Open University, take alook at our online prospectus. You can now go to Week 3. Week 3: Animals and ecosystems at the extremes Introduction Studying ecosystems in the most inhospitable places reveals a range of adaptations to survival. Desert or polar ecosystems seem remote, but their links with other ecosystems are very important. Conditions in deserts and around the poles are harsh and the organisms that live in these habitats have a range of adaptations that enable them to live there, though often on the margins of survival. So, understanding how organisms survive is part of our understanding of the ecosystems as a whole. Studying how the organisms fit into an ecosystem involves considering a number of features. You will look at the integration of behaviour anatomy, physiology and biochemistry in diverse vertebrates that live in extreme conditions. 3.1 Deserts Deserts have a unique climate, with characteristic organisms. In such an extreme environment, organisms will develop their own ‘niches’. A niche encompasses the role of an organism in a particular ecosystem, the habitat, how it eats, what it eats, and its predators. There may be empty niches in a habitat. An invader may take over a niche by ejecting the species currently occupying it. In general, two species cannot occupy the same niche in the same geographical location. In desert ecosystems, insectivorous, herbivorous and seed-eating niches are occupied by small animals, including arthropods, lizards, small birds, rodents, squirrels and shrews. Medium and large-sized animals such as hares, gazelle, camels and ostrich occupy grazing and browsing niches. Predators include foxes, e.g. kit fox (Vulpes macrotis) and cats, e.g. cougar (Puma concolor) in the deserts of the southern USA and Mexico, and Rüppell’s fox (Vulpes rueppelli) in the Arabian desert. Desert vertebrates make use of a variety of microenvironments and their associated microclimates, small-scale areas in which the climate is different from that of the habitat as a whole. For example, in a desert ecosystem, a cavity beneath a rock, a microenvironment, would have a lower ambient temperature (Ta) than the surface and hence a different microclimate. A hyper-arid sandy desert, such as the Arabian desert, has a relatively low variety of microenvironments and associated microclimates available for vertebrates. Nevertheless, the sand at a few centimetres depth is significantly cooler than at the surface, and provides a relatively cool microenvironment for animals. In contrast, American deserts such as the Sonoran have a diverse range of microenvironments, and contain a richer diversity of vertebrate species. Although our discussion here is restricted to vertebrates, you should be aware that many invertebrates, particularly insects, inhabit desert environments, and they provide an important food supply for many desert birds and mammals. 3.1.1 On size and shape The ways in which animals interact with the environment is affected by their body size and shape. One way to classify desert animals is in terms of the range of body sizes and the rate of evaporation. The logic of this classification can be appreciated by the following exercise. If you represent a small animal by a cube, and then make a larger scale model of it twice natural size, the linear dimensions of the larger animal would all be twice as large (Figure 4). However, the surface area of the model would not be increased by a factor of 2, nor would the volume, as can be seen by comparing Figure 4a and 4b. If the linear dimensions double; the surface area increases by a factor of 4 (22) and the volume by a factor of 8 (23). So the ratio of surface area to volume is lower in a large animal than a smaller one. Since heat is transferred at the surface, a small animal has greater potential for rapidly gaining and losing heat than a larger one because of its relatively large surface area. A smaller animal also has greater relative potential for evaporative water loss through its large area of skin, relative to its volume. However, animals are not cube-shaped, and certain desert species have features that can increase their surface area relative to their volume. Activity 1 Consider this question and note your answers in the box below What desert animals that you know of from your general knowledge have features that increase their surface area relative to their volume? An obvious adaptation that increases surface are is large ears and so you might have chosen the desert fox, jerboa, the jack rabbit or the elephant. A more unusual adaptation is found in the frilled neck lizard, which has a flap of skin that it can extend both for display and to regulate body temperature. 3.1.2 Behavioural strategies of evaders Small animals, classified as evaders, include desert amphibians and reptiles, and also mammals – rodents and insectivores. The term ‘evaders’ refers to the animals’ behaviour, which helps to prevent overheating of the body on hot sunny days, and avoids the need for cooling by evaporative water loss, which is not feasible for small animals living in an arid habitat. Evaders make use of microenvironments such as shady rock crevices, underground burrows and shade cast by plants, for behavioural thermoregulation. Evaders also prevent excessive cooling of the body by behaviour, retreating to shelter when the ambient temperature (Ta) plummets at night. The ultimate evaders are desert frogs such as Cyclorana spp. and Neobatrachus from Australia, which spend most of the year in aestivation, inside a burrow. Aestivation is a special kind of dormancy, which enables animals to survive lack of water and high Ta during a hot dry season. During the short rainy season, desert frogs accumulate water in the bladder, where it remains during aestivation. A famous example, Cyclorana platycephala, is known as the water-holding frog; aboriginal people used to dig up the aestivating frogs and squeeze them, in order to collect and drink the water. During aestivation, the frogs are protected from losing water to the dry soil in the burrow by a cocoon. At the end of the rainy season, the frogs burrow into the soil, and the skin undergoes a type of moulting process in which layers of epidermis are separated from the body but not shed, forming a protective cocoon, covering all parts of the body apart from the nostril openings. The cocoon thickens, becoming heavily keratinised, and prevents loss of water from the frog’s body during the 9–10 months of aestivation. At the start of the rainy season, heavy rain with consequent seepage of water into the frogs’ burrows, stimulates the frogs to emerge. Breeding and feeding occur during the short wet season. Reptiles Reptiles with a scaly keratinised skin are not so prone to evaporative water loss as amphibians, and are the vertebrates that you are most likely to see on a visit to a desert. Reptiles are ectotherms and rely on solar radiation for warming the body, and maintaining high body temperature (Tb) during the day. Desert reptiles have no problem in gaining heat for maintaining Tb at a high level on hot sunny days (Figure 7). What are the sources of energy gain and routes of heat loss for the lizard? The lizard gains heat energy via thermal radiation from the Sun, the atmosphere and the ground. Heat energy is lost via conduction from the body to the ground, by evaporative water loss, convection and thermal radiation to the sky. On a hot sunny day, more heat is gained than lost, and it is important for a desert reptile to avoid overheating. It is equally important to reduce loss of body heat when Ta plummets at night or during the winter. During the day, reptiles may move between warm and cool areas in order to maintain Tb. This movement between warm and cool areas for maintaining body temperature is called shuttling. Those species that maintain high stable Tb when environmental conditions allow by adopting heliothermic (sunbasking) strategies, are called thermal specialists. In contrast, there are some species, known as thermal generalists, which allow their Tb to fluctuate and decline, even when they could shuttle between sun and shade to maintain high stable Tb during the day, or use their burrow at night to prevent cooling of Tb to the outside Ta. Bedriagai’s skink (Chalcides bedriagai) is a thermal generalist, preferring to spend a lot of time hiding under rocks rather than basking in the Sun. The side-blotched lizard (Uta stansburiana), found in the Sonoran desert, is a typical thermal specialist. It is a small species, only 4–6 cm long when full grown. In the morning, Uta warms by basking, initially orientating itself at right angles to the Sun’s rays and flattening the body against the substratum for maximum exposure to solar radiation. When warmed Uta turns the body so that it faces the Sun while resting. Uta maintains Tb around 36–38°C. Active foraging for insects, scorpions and spiders may overheat the body, and for cooling off, especially around noon, Uta moves to the shade of rocks and scrubby bushes. Shuttling in this way enables this species to stay active during the day for most of the year except in areas where winter temperatures dip to freezing. Nocturnal desert animals A few desert reptiles are nocturnal; the Moorish gecko (Tarentola mauretanica), is found in arid regions in North Africa (also in Spain, France and Greece, so it is not restricted to deserts). Tarentola is most active for a few hours after sunset. During the night, itsTb is as low as 18°C, and can fluctuate by up to 11°C. Those lizards that tolerate wide fluctuations in Tb, even when they could use features of the environment to maintain a steady Tb, are known as thermal generalists. The Moorish gecko is a thermal generalist at night, when it is active rather than resting in its burrow. During the early morning the Moorish gecko basks in the sunlight and its skin darkens until almost black. At night the gecko is very pale. What functions and advantages do the changes in skin colour give? Dark colours absorb and radiate heat better than light colours. At night a light colour should reduce heat loss by radiation, and there is not much heat available to absorb. During the day, dark skin promotes absorption of solar heat. Although radiation to the atmosphere by the dark skin is also promoted, the energy so lost is of little significance compared to the large amount of solar heat absorbed. The advantage to the gecko of warming up in the morning is uncertain, but it is possible that a physiological process such as digestion of the food eaten during the night requires a higher Tb than the gecko can maintain at night. The ability of the gecko to vary skin colour shows that behavioural thermoregulation in reptiles is supplemented by physiological mechanisms. Sheltering in the available shade in the desert, or being active at night, are simple strategies for keeping Tb below lethal levels. In sandy desert areas, the sand itself plays an important role in behavioural thermoregulatory strategies. The Mojave fringe-toed lizard (Uma scoparia) is restricted to fine, wind-blown sand, e.g. in dunes, dry lake beds and desert scrub in the Mojave desert. Burrows in sand collapse immediately or soon after the animal has moved on, so animals buried in sand rely on air trapped between sand particles for breathing. Uma is a ‘sand-swimmer’ and its dorsoventrally flattened body and shovel-shaped head facilitate movement through the sand, which is especially important when escaping from predators such as snakes and badgers. The eyelids are protected from sand by large eyelid fringe scales. The digits have large lamellar fringes, elongated scales, especially long on the hind feet, which enable the lizards to run at speed on the sand surface. Uma grows up to about 110 mm in length, and its activity pattern is diurnal, varying according to ambient temperature. In March and April Uma is active for short periods because of the low spring temperatures in the Mojave. In summer, from May to September, the lizards are active during mornings and late afternoons, feeding on insects and plants. Sand-swimming lizards are also found in the Namib desert and include the wedge-snouted sand lizard (Meroles cuneirostris). Desert burrows Look at the way in which the surface temperature of sand can change through a day (Figures 10 and 11). Although the temperatures of sand at various depths in the Mojave desert would not be precisely the same as those in the Namib, the physical characteristics and thermal environment provided by dry sand are broadly the same in all deserts at similar Ta. A benign temperature is available below the surface at all times of the day in both seasons, in spite of extremes on the surface. These surface temperature extremes are not very different in summer and winter. The high afternoon surface temperature in winter is due to hot, dry winds (Berg winds) that reach the desert in the winter months. Burrowers Burrows provide important microenvironments for many desert evaders, and their structure and use vary between species. The desert tortoise (Xerobates agassizii) lives in deserts in the USA and Mexico, and feeds on annual herbs, cacti and shrubs, obtaining most of its water from the plants. In the Mojave desert, the tortoises live in sandy areas as well as rocky hillsides, including scrub-type vegetation, Joshua tree/yucca and creosote bush/ocatillo habitats. For the tortoises, burrows are important refuges for thermoregulation, summer aestivation and winter hibernation. Tortoise burrows in the Mojave desert are extensive and can be up to 12 m long; the same burrows are used for many generations, and are shared with other species such as burrowing owls and ground squirrels. Each desert tortoise may use up to 12 burrows in its home range and each burrow is used by different tortoises at different times. For short rest periods during the day tortoises dig shallow depressions, known as pallets, which barely cover the carapace. Bear in mind that when occupied by a tortoise, a burrow’s relative humidity may rise to 40 per cent because of the tortoise’s water loss by evaporation from the lungs, exposed skin and eyes. Stable Ta and humidity in the burrow protect the tortoise from extremes of high Ta and from winter frosts. It was noticed that tortoises are fussy about the burrow selected for resting. At the end of foraging, tortoises were observed to enter and leave several burrows before settling. Mojave desert tortoises are active between March and June, a time when the winter rains have stimulated the growth of annual plants, providing abundant food for the tortoises. The tortoises begin foraging during the morning but usually by noon they have moved into pallets and burrows to shelter from high Ta. At night, burrows provide shelter from low Ta and also protection from nocturnal predators such as kit foxes and badgers. By the end of June, when surface temperature may reach 60°C, and annual plants have dried up, the tortoises retreat to their deep burrows and aestivate, a behaviour that helps to conserve body water. During aestivation, up to a quarter of the tortoises’ body mass may be water stored in the bladder. Occasionally an aestivating tortoise emerges to drink during summer thunderstorms. In the eastern Mojave desert tortoises are active for most of the summer because there, summer rainstorms provide sufficient new plant growth. For their winter hibernation, tortoises aggregate in the burrows; up to 25 individuals have been found in one burrow. Hibernation lasts from October to the end of February, and during this time Tb of the tortoises is the same temperature as the burrow, around 5–16°C in winter. Note therefore that hibernation in the desert tortoise is not the same physiological process as it is in hibernating mammals . Reptiles do not regulate Tb physiologically during hibernation; Tb is the same as burrow Ta. You will find that in some references, reptile ‘hibernation’ is termed ‘brumation’. Mammalian desert burrowers You may be surprised to learn that like desert ectotherms, small desert rodents also depend on burrows for thermoregulation. Merriam’s kangaroo rat (Dipodomys merriami) is a typical evader, living in the Sonoran desert, Arizona, and in Death Valley, California, two of the hottest and driest areas in the Western Hemisphere. Individuals live in a maze of burrows, which they defend. They remain in their burrows during the day, and often plug the entrance with soil. At night kangaroo rats emerge from their burrows for just two hours to collect seeds, in particular seeds of the creosote bush, which they push into their cheek pouches, returning at intervals to empty the food into their burrow. In this way, food caches are built up; kangaroo rats always eat inside the burrow, drawing on their food cache. Inside the burrow, the air is cooler and more humid than above the ground, as moisture from respiratory water loss accumulates. Measurements made on similar burrows in the Negev desert, Israel, showed Ta of around 26°C at 1 metre depth for 24 hours per day when ambient temperature above ground ranged from 16–44°C. However, not all small desert animals can burrow. The desert wood rat (Neotoma lepida) lives in deserts in the southern USA, including Death Valley, California. Wood rats do not burrow but build elaborate houses around the base of cacti or shrubs, amongst a patch of agaves, or beneath a rock outcrop. Wood rat houses can reach huge sizes and their interior is significantly cooler, by about 5°C, than the outside during the heat of the day. Desert wood rats shelter in their houses during the day, and emerge to forage at night, eating creosote bush, cholla, prickly pear cactus and agave. 3.1.3 Behavioural strategies of evaporators Evaporators are animals that depend on sufficient water intake to enable them to cool Tb by evaporation. Few of these species can survive in deserts, and those that do either live on the edges of deserts where they can access water, or have behavioural and physiological adaptations that reduce reliance on evaporative cooling. So for evaporators, evasion may be an important part of their thermoregulatory strategy. Evaporators include medium-sized mammals such as jack rabbits, dogs, foxes, and also desert birds such as larks. The jack rabbit (Lepus californicus) is a hare, living in the Sonoran and Mojave deserts. Jack rabbits do not burrow, although they are quite small, weighing about 2 kg. A jack rabbit would need to lose at least four per cent of its body mass per hour to thermoregulate by evaporation. There is little or no free water around; water is obtained from the diet, green plants, including cacti in the summer. The classic work of Knut Schmidt-Nielsen (1965) showed that behaviour is important for the jack rabbit’s survival. During the hottest part of the day the animal chooses a shaded depression in the ground, often in the lee of a bush, in which it crouches (Figure 6). The bottom of such a depression has a much lower temperature than that of the rest of the surface, the hot desert wind and much of the radiation passing over the animal’s head. From its sheltered position, the jack rabbit’s large radiator-like ears can be exposed, not directly to the Sun, but to a clear blue sky. The radiation temperature of the north sky at midday is only 13°C so if the ears, which are richly vascularised, have a temperature of 38 °C, and have a surface area of 400 cm2, are directed towards the sky, they can radiate about 13 kJ h−1, which is about half of the animal’s metabolic heat production. The jack rabbit forages during the night. The kit fox (Vulpes macrotis) lives in the Sonoran, Mojave and Great Basin deserts in southwestern USA. Kit foxes have very large ears, which are thought to provide an increased surface area for cooling the body. They are carnivores, and hunt at night, preying on kangaroo rats, tortoises and jack rabbits, and occasionally catching ground-nesting birds, reptiles and insects. They reduce evaporative water loss by spending the day in underground dens, emerging at sunset to begin hunting. The physiological importance of dens for desert foxes should not be underestimated. By remaining in the den during the day, a desert fox reduces drastically the need for panting, a mechanism used by foxes and dogs for cooling the body by evaporative water loss. A few species of small birds live in the most extreme deserts. Dune larks (Mirafra erythroclamys) are the only birds that live year round in the Namib sand sea, one of the driest regions of the world. Dune larks feed on insects and spiders, which they collect during the day, while walking over the sand surface; they also peck insects from just below the sand surface. In winter the birds feed on seeds blown in from adjacent grass land. The scarcity of water in the Namib sand sea means that dune larks drink rarely and the birds rely on water in their food and on metabolic water. Birds do not sweat, but they use both cutaneous and respiratory evaporative water loss for cooling the body. During the hottest part of the day, from around 12.00 to 15.00, dune larks seek shade and stand still. Presumably this behaviour helps the birds to cool Tb and reduces evaporative water loss. Taxidermic mounts have been used to determine operative environmental temperature, Te, for the birds. Te is the temperature that an animal would reach in the environment if it was biologically inactive, i.e. only the physical characteristics of the animal are taken into account. It is defined, in physical terms, as the temperature of a black body of uniform temperature, in an identical situation to that which the animal occupies, with the same values for conduction, convection and radiation. As the definition is purely physical, it is possible to make models of animals and to use them to measure Te experimentally. The results of these experiments suggest that in winter, the strategy of finding a shady spot during the hottest part of the day lowers Tb sufficiently, so there is no need for physiological cooling, in particular evaporative water loss, for maintaining Tb While desert animals classed as ‘evaporators’ could use evaporative cooling for maintaining Tb at high Ta, the need for this is avoided by simple behavioural strategies. Nocturnal foraging and daytime use of dens, burrows and shade for cooling reduce the need for physiological cooling by evaporative water loss, thereby conserving water. 3.1.4 Behavioural strategies of endurers Endurers are defined as large desert mammals such as oryx and camel, and large desert birds, including ostrich and emu. The term ‘endurers’ suggests that these animals are forced to endure the extreme conditions of the desert climate because they cannot shelter from high Ta and intense solar radiation during the day or low Ta at night, as they are too large to hide in burrows or dens. Nevertheless, in spite of their size, endurers do take advantage of aspects of the environment for cooling by means of behavioural strategies. Large mammals tend to be inactive during the hottest part of the day, thereby reducing metabolic heat production. The Arabian oryx (Oryx leucoryx) lives in the Arabian desert, including areas where free-standing water is rarely if ever available. On hot days oryx dig into the sand with their hooves, exposing the cool sand below the surface, and sit in the depressions. Body heat is lost to the cooler sand by conduction. Where possible, the oryx also spends time sitting in the shade of evergreen trees (Maerua crassifolia) during the hottest part of the day. Oryx forage at night during the summer, avoiding exposure to high Ta and intense solar radiation. They feed on grasses and rely on the water content of the plants for their intake of water. Dorcas gazelle (Gazella dorcas) live at the borders of the Sahara desert and are the smallest species of gazelle, weighing just 15–20 kg. They have very long limbs in proportion to their body size, and large ears: both features maximise any convective cooling caused by breezes. Dorcas are described as the most desert-adapted of all gazelles, as like the oryx, they are reputed to be able to survive without drinking any water at all. Their feet are splayed, an adaptation for walking and running on sand. Dorcas gazelle graze and browse at night and at dawn and dusk, feeding on leaves, flowers and pods of acacia trees, and using their hooves to dig for bulbs. Long limbs, tails or necks provide large surface areas from which heat can be dissipated, and behaviour patterns may maximise loss of heat from these areas. The ostrich (Struthio camelus) is the largest living bird, weighing up to 150 kg. Ostriches forage during the day. The birds select plants with high water content when grazing, especially during times of water shortage. The naked neck of the ostrich and its long naked legs provide a large surface area for convective and radiative cooling, especially in breezy conditions. The ostrich uses behaviour to enhance the cooling effects of feather erection at a high ambient temperature and incident solar radiation. Sparsely distributed long feathers on the dorsal surface of the bird erect in response to warming of the skin, thereby increasing the thickness of the insulation between solar radiation and skin. The gaps between the feathers allow through air movements, which cool the skin by convection. The birds supplement the physiological response during the hottest part of the day by orientating themselves towards the Sun and bowing out their wings away from the thorax, forming an ‘umbrella’ which shades the exposed thorax. The naked skin of the thorax acts as a surface for heat loss by both radiation and convection. At night when ambient temperatures plummet, ostriches conserve heat by folding the wings close to the thorax and tucking the naked legs under the body while they sit on the ground. The dorsal feathers respond to low Ta by flattening and interlocking, which traps an insulating layer of air next to the skin, and keeps most of the skin at 34.5° C. Evaporative water loss is the most effective means of reducing body temperature during heat stress. However, in deserts, very little, if any, free-standing water is available. For all groups of desert vertebrates, behavioural strategies for maintaining Tb play a crucial role in preventing overheating of the body, which reduces the need for evaporative cooling and thereby conserves water. In the following section, we will see how in desert vertebrates, behavioural strategies for controlling body temperature are integrated closely with biochemical and physiological mechanisms. Desert animals are classified in terms of their body size and physiology into three groups: evaders, evaporators and endurers. The logic for this classification is that the smaller the animal, the larger its surface area to volume ratio. Small animals therefore gain and lose heat faster than large animals, warming rapidly when exposed to intense solar radiation, and cooling rapidly at night. Small endothermic evaders, e.g. kangaroo rats, rest in cool microenvironments, e.g. shade or burrows, during the day. Lizards, ectothermic evaders, regulate Tb during the day by shuttling between sun and shelter. They avoid night-time hypothermia by resting in burrows. Nocturnal evaporators, e.g. kit foxes, remain in cool dens during the day. Some endurers, large species such as the oryx, graze nocturnally in summer, sitting in shade during the day. Behavioural strategies for avoiding intense solar radiation link intimately to physiology. Such behaviour prevents large fluctuations in Tb and conserves water by removing the need for evaporative cooling, which is of crucial importance in deserts where water is scarce. 3.1.5 Camels and humans as desert dwellers Both humans and camels live in desert conditions and both rely on evaporative cooling to regulate their body temperatures. However, as this classic Open University video makes clear, the camel handles its water balance better than humans do, as well as having other adaptations that help it survive in a desert ecosystem. Camels and humans as desert dwellers [MUSIC PLAYING] NARRATOR The hot, dry conditions of the desert are inhospitable to most mammals because they cause overheating and dehydration. Yet, t8hese camels are desert dwellers, and compared to the men riding them, they're well-suited to a desert environment. The camels in this Jordanian desert patrol can travel up to 20 miles a day for 15 days without water. But their riders need to have regular stops for water and shade throughout the day. [SINGING] Such different abilities to cope with heat stress must lie in their physiological makeup. One built-in advantage for the camel is the extensive insulation provided by its fur coat. The fur acts as a heat barrier, helping to slow down the transfer of radiant and convective heat from the outside to the inside. To provide similar insulation, the men must wear suitable clothing. But they can't always compensate for being ill-adapted to this environment. Consider what problems in relation to temperature man faces in the desert heat. Also, what other adaptations, besides insulation, might the camel display? For instance, another advantage the camel has over man is revealed by a study of the fluctuations in body temperature throughout the day. The body temperature of a man rises to a critical level in only a few hours' exposure to desert heat. To lower this temperature, the man begins to sweat as a means of losing heat. The body temperature of the camel continues to rise past man's lethal limit, and the camel can sustain temperatures as high as 40 degrees centigrade without sweating. Not only does the camel have the ability to tolerate higher body temperatures than man, but its larger size allows it to store a larger amount of heat. The net effect is that it can postpone the onset of sweating, and in doing so, save a considerable amount of water. For the men to avoid losing too much water, their only alternative is to seek shade when it's available. By allowing its body temperature to rise by six degrees centigrade, the camel saves as much as four litres, or seven pints, of water. But if the heat load were maintained, then eventually the camel would have to sweat, and it, too, would become prone to dehydration. Dehydration is one of the major dangers facing mammals in the desert, and water holes are essential stops on a journey. [WATER RUNNING] As you might expect, desert-adapted animals tolerate dehydration very well, and can lose as much as 40% of their body weight without serious damage. But for man, the upper limit of tolerance is only 15% of his body weight before serious side effects are seen to interfere with blood circulation. Normally, the blood moves heat around the body, and exchanges heat to the outside of the skin surface. Dehydration causes rapid loss of water from the blood. The volume of the blood falls, it becomes more viscous, and the blood vessels contract. The result is that the heart has to work harder to pump the blood around the body. The effort becomes so great that the circulation becomes sluggish, and it's less efficient at moving heat to the skin's surface. As less heat is lost to the outside, the body temperature rises explosively. The camel, even under severe dehydration, loses water mainly from its stomach and large intestines, so the volume of the camel's blood changes very little, and is still able to transport and exchange heat efficiently. At the end of the day's journey, the camel's body temperature will be relatively high. As it's unloaded, the falling air temperatures of early evening give it the perfect opportunity to dump some of the heat it's stored during the day, and replenish itself with water. And where water is available, it can rapidly take it on board. A deficit of about 20% of its body weight can be made good within 10 minutes. In this time, the camel is able to drink something like 70 to 100 litres of water. That's equivalent to a man drinking 20 litres, or 30 pints. [SPEAKING A FOREIGN LANGUAGE] Air temperatures in the desert at night can fall very low. And whereas the men try to keep warm, the camel starts dumping its heat. Like a night storage radiator, it stores heat in the day, and gives it up at night so that by morning, it starts with a relatively low body temperature. So the secret of the camel's tolerance of desert conditions has nothing to do with its infamous hump, where fat is stored, not water. As we've seen, its success as a desert dweller relies upon physiological adaptations to heat stress and dehydration. 3.2 Cold environments The Arctic regions are the exact opposite of deserts as far as severe climate is concerned. Organisms in the Arctic regions have adapted to habitats influenced by extreme cold, resulting in short growing seasons for plants, land that produces little food, and lack of shelter. Some animals migrate and thus avoid the extreme cold for large parts of the year. At high latitudes, the Sun’s rays always strike the Earth at a large angle from the vertical so they travel through a thicker layer of atmosphere and are attenuated by the time they reach the ground. Because the Earth’s axis of rotation is inclined to its path around the Sun, there are large seasonal changes in day length and the Sun is continuously below the horizon for a period in winter and continuously above the horizon for an equivalent period in summer. The range of annual temperature change is much greater at higher latitudes, and in mid-winter (January and February), the range about the mean is more than 12 °C. In polar climates, the temperature can change abruptly and often unpredictably. In coastal areas, the sea keeps the climate much more equable. Further inland, fluctuations in temperature are even greater. Polar organisms are thus adapted both to the extreme cold and to abrupt fluctuations in temperature. The Arctic Circle (66° 30′N), and the equivalent latitude in the Southern Hemisphere, are defined as the latitude above which the Sun is continuously below the horizon for at least one day each year. Warm, moist air from the temperate zone rarely reaches high latitudes, so in most polar areas precipitation is low. Much of the water is locked away as ice, which has a low vapour pressure, and the air is very dry (often as dry as a tropical desert) and ground water is inaccessible to plants as well as to animals. Terrestrial environments in the Arctic are, by geological standards, relatively new, most of the land having been completely covered with a thick layer of ice as recently as 10 000 years ago. Consequently, the soil is thin and fragile, and poor in organic nutrients. The optimum temperatures for plant growth do not coincide exactly with peak sunshine. At Longyearbyen, continuous daylight begins in late April, but the mean temperature does not rise above 0 °C (and so the snow and ice do not melt) for another two months. These circumstances, combined with the severe climate, mean that the growing season for plants is short but intensive, and total productivity on land is low, producing little food and still less shelter for animals. 3.2.1 Life on land at high latitudes Relatively few species of terrestrial organisms live permanently at high latitudes. For example, although the land area of Svalbard is about 62 000 km2, almost half that of England, there are only a few hundred species of insects and other invertebrates, two resident terrestrial mammals, the arctic fox (Figure 17a) and reindeer (Figure 17b), one bird (an endemic species of ptarmigan) and no reptiles, amphibians or completely freshwater fish. However, many other species spend part of the year on or near the land, often while breeding or moulting: seasonal visitors include more than 30 species of migratory birds (various kinds of geese, auks, puffins, skuas, terns, gulls, and eider ducks and snow buntings), and mammals that feed in the sea, such as polar bears, walruses and several species of seal. The simple ecosystem on land and the severe, erratic climate tend to produce ‘cycles’ of population abundance followed by mass mortality or migration (e.g. lemmings in Scandinavia and Russia). Interesting physiological and behavioural adaptations to these fluctuations in food supply have evolved in some of the larger animals. The vast continent of Antarctica has no indigenous terrestrial vertebrates, although many birds, including penguins, skuas, terns and gulls, and six species of seal spend time on or near land. Only two species of terrestrial mammal occur naturally throughout the year on Svalbard (although a few others have been introduced by humans during the past century). Figure 17a shows the arctic fox (Alopex lagopus), which also occurs throughout the Arctic, and in mountains at lower latitudes. The picture in Figure 17a, taken in late autumn, shows an adult in its long, dense winter coat. The summer coat is usually greyish brown, often with white markings. Alopex is bred in captivity for its fur, which can vary in colour from grey to bluish in winter, and chocolate brown to fawn in summer, hence the common names, silver fox or blue fox. Figure 17b shows a subspecies of reindeer (Rangifer tarandus platyrhynchus) that is endemic to Svalbard. This picture was taken in July, when the vegetation is at its highest, and this young male is growing antlers for the mating season in September. The situation in the polar seas is very different, which you will discover as you conclude your study of extreme ecosystems by learning about life in the polar seas. 3.2.2 Life in the polar seas Life in the polar sea ice forms part of a web of interactions, which Dr Mark Brandon discusses with Brett Westwood as he considers the tiny life trapped in the sea ice that is the foundation for the entire food chain at the poles. Life in the polar seas INTERVIEWER Mark, ice doesn't behave the same way at the different poles, does it? So how does it vary? DR. MARK BRANDON Well, one of the things that affects the ice most of all is the basic geography. In the Arctic, you've got land and then a deep ocean in the middle. Whereas in the Antarctic, you've got land in the middle and deep ocean around the edge. If you go back to the Arctic, in winter, all of that Arctic Ocean gets frozen over with what we call sea ice, which is a very thin layer of ice, only perhaps two or three metres thick. It extends out - about 15 million square kilometres of the ocean gets covered by this sea ice. And it is a bit like if you think of polystyrene floating on the sea, it gets blown about by the wind. So the sea ice is constantly moving and constantly drifting around and grinding up. So if you hear about ice being thicker that three metres, it's usually two ice flows of three metre thickness that bumped into each other, one on top of the other. INTERVIEWER So all this floating ice in the Arctic, it does collide, I would imagine. It forms ridges, does it? DR. MARK BRANDON It does. And if you actually go online, there's the International Arctic Ocean Buoy Project, IOEB. And you can actually look at the drift tracks of buoys that are actually out there right now, sending back weather data from the Arctic Ocean, that drift with the sea ice. and so you can look at these fantastic movies of how the ice drifts. INTERVIEWER How does ice behave in the Antarctic, not in the same way then? DR. MARK BRANDON Well, the seasonal change between the Arctic- in the Arctic, about 2/3 of the ice disappears between the summer and the winter. In the Antarctic, almost all of the ice disappears in Antarctic summer. INTERVIEWER Where does it go to? DR. MARK BRANDON It melts away. So there are only a couple of small areas, mainly the Ross Sea and the Weddell Sea and quite close to the coast. Because when I say most of the ice disappears, there's about 2 million square kilometres of ice still in the Antarctic. But compared with Antarctic winter, that 2 million square kilometres of ice grows another 15 million square kilometres. So it really is just the remnants of a vast amount of ocean covered by ice. INTERVIEWER And for the permanent ice, we're talking about some incredible thicknesses as well, aren't we, in the Antarctic particularly? DR. MARK BRANDON Well, if you look at Antarctica, it's a continent. It's land. And then snowfall, over millions of years, gets compressed and turned into ice. And individual layers of this snow build up thickness of ice. And this started happening, this snowfall, maybe 35 million years ago. And the thickness of ice now, on East Antarctica, the east part of Antarctica, is about three kilometres thick. And that's made entirely of snow. So it's fresh ice. It's the sort of stuff that, when it reaches the edge of the continent, this land ice, it can either form an ice shelf, which is a large, thick shelf of ice, perhaps 200 or 300 metres thick. Or the glaciers can fall straight into the sea and form icebergs. Whereas the sea ice is just frozen seawater, and so anything that's in the sea water gets trapped within the ice. And it's quite a porous thing, sea ice, compared with land ice, because it's formed from ice crystals growing in the water, rather than snowfall being compressed. INTERVIEWER So there's life within this sea ice. Seawater freezes at −1.9° C, but because of the anomalous relationship between the density and temperature of water, ice floats, insulating the water underneath from the cold air above. Except in very shallow areas, the sea-ice does not extend to the sea-bed, even at the North Pole. Storms and currents sometimes break up the ice, creating many temporary, and some permanent, areas of open water even at high latitudes in mid-winter. Such turbulence also oxygenates the water and admits more light, making the environment much more hospitable to larger organisms. The movements of ocean currents are complex and may change erratically from year to year. This often results in an upwelling of deep water rich in nutrients and promotes high primary productivity in the sea. In most arctic regions, the sea is both warmer and more productive than the land. So at high latitudes there are many more organisms in the sea than on land, at least during the brief summer, and, as in the case of the baleen and sperm whales, some are very large. Krill You heard previously how Dr Mark Brandon and colleagues studied krill under the sea ice. In this video scientists from the British Antarctic Survey (BAS) are trawling for krill and sorting them for later analysis – some task! As you watch listen out for answers to the following questions: What is the role of krill in the Antarctic food chains? How do the food chains in the polar seas compare with those introduced earlier by Professor David Streeter in the oak wood? Krill DR. DAVID ROBINSON: This huge net is being used to trawl the polar seas for krill, as part of a research programme. In the folds at the bottom of the net are thousands of these prawn-like crustaceans. Krill are a key component of the main food web in the southern oceans. MALE SPEAKER 1: Do you want me to-- MALE SPEAKER 2: In the net too. MALE SPEAKER 1: Yeah. MALE SPEAKER 2: I think there'll be more water on deck tomorrow morning. DR. DAVID ROBINSON: They're an essential source of food for numerous animals, from fish and birds to the largest of the whales, the blue whale. In recent years, krill have even been harvested commercially. FEMALE SPEAKER: Yeah. MALE SPEAKER 3: Is there anything on that or is it just a surface layer of krill? DR. DAVID ROBINSON: Sorting the sample is a painstaking task, as the scientists pick out individual krill to place them in trays for later analysis. 3.3 Apply your knowledge of ecosystems A number of interesting points came out of the previous section. Consider some other, wider questions about possible changes in the ecosystems and how they might affect life in the polar regions. For this activity you may need to draw on your general knowledge at that of others, in addition to your understanding of the course so far. Go to the Week 3 forum and discuss the following questions. What kinds of physiological adaptations to fluctuating food supply have organisms in the Arctic regions made? What kinds of behavioural adaptations do organisms in the Arctic regions have that specifically suit the ecosystems they are a part of? How do emperor penguins’ breeding patterns fit the harsh ecosystem they are a part of? How would leopard seals be affected if the penguin population experienced a boom or a decline? What would this mean for the rest of the ecosystem they are a part of? 3.4 Week 3 quiz This test is about the physical characteristics of extreme ecosystems and the adaptations that some animals have to the harsh conditions. Complete the Week 3 quiz now. 3.5 Review of Weeks 1 to 3 These three weeks have introduced you to the concept of an ecosystem and the debate about how to set the boundaries of such systems. Energy is the key link within ecosystems and the pathways by which energy flows can be explored within an ecosystem by examining the food chains that are present. In some types of ecosystem the food chains are long, complex and many-branched. In the polar seas you have found that they can be very short, such as the 3-step chain from plankton, through krill to the largest animal on the planet, the blue whale. Some of the examples of animals in ecosystems have introduced you to the concept of adaptation. You saw squirrels flying through the air and may in your discussion have linked their adaptations to those of other animals, such as the flying lizard and the flying snake. These adaptations to gliding enable faster travel through the complex, forest environment. Gliding shows how similar solutions can arise during evolution in unrelated groups of organisms. In the second half of this course you will be looking at the impacts humans have on ecosystems, but major events occurring on the planet may also have impacts. Volcanic eruptions and tsunamis are obvious examples. This video shows a large scale event in an ice sheet in Antarctica. The effect on the area itself is substantial, but could it have wider implications? This is a larger question which you should ponder on and come back to when considering human impacts on ecosystems. Large scale change DR DAVID ROBINSON The Wilkins Ice Shelf on the Antarctic Peninsula covers an area similar to that of Jamaica. In March 2008, the ice shelf began to break up. A Twin Otter plane from the British Antarctic Survey flew over the ice shelf and took these dramatic pictures. Flying low over the massive cracks in the ice sheet revealed the scale of the breakup. Large pieces of broken ice were now floating on their side. Since 2008, the breakup has continued. A continuing theme has been that of conservation. How do you study ecosystems and then conserve them? Conservation raises a whole series of questions. For example, should conservation efforts be concentrated at the individual species level or should they all be directed to conserving habitats? Take this question away with you as you finish the next three weeks of the course. You will appreciate that there is no simple answer, but if you know what you have in an ecosystem then at least you can start to decide what action to take to conserve it. Identifying animals, plants and fungi is, therefore, an essential part of the study of ecosystems. Next week, you will take part in an activity about identifying organisms in an ecosystem, using the iSpot website to post observations. If you would like a short break or tofind out more about animals living at the extremes visit our Ecosystems area on OpenLearn. You can now got to Week 4. Week 4: The unseen world Introduction This week you will learn about the smaller organisms at the base of food chains in simple and complex ecosystems. Then look for organisms in your own area and identify them using the iSpot community. Three-quarters of the Earth’s surface is covered with water, and that water is full of particles and a vast array of different kinds of creatures make their living by filtering those particles out of the water. There are many very small organisms that inhabit the water world. Understanding their lifestyle and inter-relationships requires us to understand their biology, but also something about the physical nature of the environment in which they find themselves. We are dealing with a different world at the level of the very small. In the following audio Dr Aaron Bernstein talks to Brett Westwood about some of the wonders of the microbial world and how it redefines our understanding of life. Listen out for answers to the following questions: Dr Bernstein compares the living world with a tapestry. Why does he regard this as a useful analogy? Why is it a problem to define species in the microbial world? Ocean ecosystems BRETT WESTWOOD Let's get a feel for what we mean in this international year of biodiversity, just what we mean by biodiversity, the sheer scale of it. DR. AARON BERNSTEIN Yeah. Biodiversity is a wonderful term, because it takes something that's extraordinarily broad and focuses it into a single word. And really, what that word represents is all life on Earth and its variety. When people who have heard the term before - heard the term biodiversity - they tend to conjure images of individual species, like lions and tigers and bears. But really, it's much bigger than that. It includes the smallest life forms, the microbial world, on up to the largest creatures on the planet. But importantly, it also includes the diversity of communities they form. And scientists call these things ecosystems. But that is also another important form of biodiversity. BRETT WESTWOOD The sheer scale of this unseen, the microworlds of biodiversity, actually baffles me. Have we got any idea about how immense it is? Or is it impossible to quantify? DR. AARON BERNSTEIN Well, we know it's immense enough such that the diversity of genes in the microbial world - we know that that is far greater than the diversity of genes in the rest of the living world. But really, we're utterly ignorant about the microbial world. In fact, it is the last great unexplored frontier in life on Earth. And just in the recent past have we started exploring it with any amount of force. BRETT WESTWOOD Well, I read something the other day that said there was something like in 30 grammes of soil in a Norwegian conifer forest, there was something like 500,000 species estimated of microbes or bacteria, including everything. How on earth could we possibly grapple with sort of figures? DR. AARON BERNSTEIN That's a good question. The wonder of the microbial world is that it continues to redefine our understanding of life. We, as large creatures in the scheme of life, tend to think that species are other large things. And so when we think about the microbial world, we try and put these concepts of what life forms are onto these small organisms. And it turns out that identifying even a species of a microbe is a rather challenging task, because microbes, it turns out are quite promiscuous. And they swapped genetic material all the time. In fact, it may come as a shock to some people listening to this programme that in fact, there are significant portions of our own genes that come from microbes. And they have, over time, managed to get their genes into us. But the diversity in the microbial world of the genes is profound, and not just in terms of the awe that one gets when considering how much diversity is, but also in terms of its relevance to human well being. BRETT WESTWOOD Well, you've touched on how it affects us. I just want to go back to what you were saying, then, about species concepts. We know when a blackbird or a robin is a blackbird or a robin. What about microbes? Are they continually changing? Can we put them in species boxes in the same way that we often do with larger animals? DR. AARON BERNSTEIN Right. It's proven that the definitions we've used to define species of big organisms just don't seem to fit very well for the microbial world. We have these definitions of species that are based upon appearance for species. So if one organism looks like another organism, that might mean they're the same species. We also use definitions based upon reproduction - so if two species are capable of mating and producing fertile offspring. But really, those definitions don't work hardly at all in the microbial world, because of course, most microbes don't have sex, or at least not in the way most people would consider it. And they oftentimes will look very similar under a microscope, and yet their genetic material is profoundly different. So it's been a great challenge to biologists to come up with meaningful definitions of essentially what would be a species in the microbial world. And really, there's still an ongoing debate as to how best to do that . BRETT WESTWOOD So they're not playing it by the rules we already know and the rules we attach to larger organisms. But are they changing as well? Is there evidence that, as well as not necessarily playing by those rules, they're also evolving as we observe them? DR. AARON BERNSTEIN Absolutely. There's some fundamentally different biological processes that occur in the microbes of the world than in higher organisms. And some of those different processes allow them to change much more deftly than higher organisms. And that really gets down to the most molecular level. The machines that they use that copy their genomes are much less accurate than those in higher organisms. And so their rates of mutation in their genomes tend to be much higher. And that enables them to adapt to new environmental circumstances. I see this as a doctor all the time in antibiotic resistance. So there are bacteria that infect humans which have become resistant to many different antibiotics. One of the most widely known is methicillan-resistant staph. aureus, or MRSA. The bacteria is called Staphylococcus aureus. Methicillin is an antibiotic class. It's a group of antibiotics or defines a group of antibiotics that used to readily kill this bacteria. But because the bacteria evolve so quickly under pressure - under pressure, in this case, from antibiotics - there are some of them that have mutated to become resistant to this antibiotic. And so as a paediatrician, when I take care of children, this has become a major issue for our ability to treat what used to be a really rather easy, treatable bacteria. But of course, this ability to change their genomes has had enormous influence in other ways. There's another bacteria that lives in hot springs called Thermus aquaticus. It was originally discovered in the Yellowstone National Park in the United States, living at about 70 or so degrees Celsius. That's a temperature that would cook us alive, but these bacteria call it home. And they're able to do that because the copy machine they use to replicate their genome works just fine at that temperature. In fact, that's near its optimal temperature. And that machine produced by that bacteria is the basis for a diagnostic test called the polymerase chain reaction. It's the basis of all of these crime show lab scenes in which they're trying to sort out who the criminal is. And they use this technology called PCR, polymerase chain reaction, to identify criminals. We use it to test for infectious diseases. It has been described as the single greatest discovery in biology of the 20th century. And this is all because of this bacteria's ability to adjust its ability to live based upon evolution and its ability to change its genome. BRETT WESTWOOD I want to move on a little bit now just to talk about diseases that occur, things that come in from the outside. We've talked about heritable microbes. What about the proportion of disease and microbes that affect us that have a life cycle outside people? Because the more we change their world, then, and the more we change the world outside us, surely the more vulnerable we are to receiving infections from those pathogens, from those creatures. Can you talk a little bit about that? DR. AARON BERNSTEIN Sure. I hope everyone's sitting down, because it turns out that while we like to believe that when we get sick, we caught it from our work colleague or from our child or from someone we sat next to on the train, it turns out that although the source of that illness to us is most often from another person, a majority of microbes that cause disease in humans in fact have life cycles that, as you point out, include species other than ourselves. In fact, if you look at the 1,400 or so known pathogens of humans, probably 60% to 70% or so fall in that category. But what's interesting is that the new pathogens, the so-called emerging infectious diseases - these include both diseases that we've known for a long time such as tuberculosis that are spreading around the world, but also entirely novel microbes, such as SARS or the H1N1 virus. If you look at so-called emerging infectious diseases, that percentage gets even higher. And it raises the question as to whether changes to ecology on a much grander scale, as you point out - ecosystems around the earth - may be playing a role in disease emergence. And there's certainly evidence to suggest that, particularly with SARS, for example, but also with other emerging infections-- that because these microbes inhabit organisms that are not humans, that changes to the ecosystems that those organisms live in may in fact cause them to change where they live, and in some cases, that leads them to move into humans, where they had not been in the past. BRETT WESTWOOD So an example for that, for example, something like H5N1, which was caused by the proximity of poultry or birds to us? DR. AARON BERNSTEIN That's right. So the flu virus, people refer to H1N1 as the swine flu and H5N1 as the bird flu. Well, it turns out that flu viruses infect lots of different organisms. And they tend to actually be like first cousins. So what distinguishes a swine flu from a bird flu from a human flu is really which organism the virus infects best; which of course, has to do with the genes within that virus. But as I was mentioning, with microbes, and particularly with viruses, their genomes mutate quite readily. And so when their genome is able to mutate and change, it changes the potential with which they may infect a different species. This is exactly what happened with H1N1. The flu virus has eight strips of genetic material in it. And the H1N1 virus, in order to make it be capable of infecting humans, swapped out one of those eight segments. And that new segment of its genome, essentially, was the trigger that enabled it to move. Now, where exactly that got introduced and how it got introduced is shrouded in mystery at this point. But we know from past flu pandemics that the flu virus swaps pieces of its genome in and out among pigs and ducks and humans and other creatures that happened to be put in close proximity. So it would not surprise me at all that the event that led to this new flu emergence was due to some concurrent exposure of multiple species to this virus that enabled two different varieties of the virus to get very close to each other and swap their genetic material. BRETT WESTWOOD So the message from us is that we're not separate from the natural world. We're not separate from ecosystems out there. We're part of them, and we either pay the penalty or reap the reward, depending on how closely involved we are and how we modify those. DR. AARON BERNSTEIN Right. The image I like to think of when it comes to our relationship to nature is that really, the entire living world, including us, is like a tapestry, and that we are as enmeshed in that tapestry as any other organism. And as you're well aware, the amount of biodiversity on Earth at present is declining at a rather impressive and alarmingly impressive rate. And so this tapestry is essentially getting strands yanked out of it. And we are trying our best to shine flashlights on various corners of this tapestry to understand our relationship to it. But really, we don't understand it very well at all. And so we don't know which strands that get pulled out are going to affect us, nor do we really understand the composition as a whole, because we only are able to glance at various small pieces of it. And as much as we try to pull ourselves out of this tapestry to make ourselves believe that we're independent of nature, nature is continuously pulling us back into it and reminding us-- through these outbreaks of infectious disease, through our difficulties with supplying food, through the antimicrobial resistant problem. We try and convince ourselves, kid ourselves that we can live apart from nature. And yet, the more we do that and the more we act in that way by degrading ecosystems, decreasing natural habitats, influencing the global climate, the stresses upon the fabric of life yank us back to it. 4.1 Seas, ecosystems and small organisms Many very small organisms live in water. Understanding their lifestyle means understanding the physical nature of the environment, because it is a different world for the very small. 4.1.1 Investigating small organisms In the next video you will be able to watch a marine scientist collecting plankton samples in a hi-tech way, but first listen to some background to the work as David Robinson talks to Penny Boreham about small organisms. Some of the planktonic organisms are single cells whereas others, such as the young stages of larger animals like crabs, are multicellular. In the interview, you will also hear about an organism called ‘Tony’. Tony is found in a very unusual ecosystem – one that you may not have thought about before – and you will learn more about this in the video entitled ‘Investigating flagellates’. Investigating small organisms DR. DAVID ROBINSON I'm David Robinson, and I'm a biologist at The Open University. And in this series of clips, we're going down into the world of the small organism, organisms that normally we're not aware of. So when you look out to sea, you see masses and masses of water, and you're just not conscious of the huge number of organisms that are in only a small volume of that water. One of the most interesting things you do when you start out in biology by the sea is just take a net and sweep it through that water. And then take your net out and wash off everything that you've got in your net. And you find you've got a whole world in your bottle of tiny organisms. And it's a completely different area of study. Because they're small, you require very different techniques to study them. And because they're so small, and they're completely immersed in their environment, the environment has great influences on them that you might not suspect until you study them. INTERVIEWER You just said that different methods are needed for working with small organisms. What type of instruments or methods are needed? DR. DAVID ROBINSON Well, firstly, of course, there's microscopes in order to magnify them and see them. But I think some of the other methods are ways of collecting them. The sea clearly is very deep. Although the plankton don't go down to enormous depths, but they do have quite a vertical distribution. And if you want to sample at a particular depth, you have to be able to send your bottle down there, collect water at that depth, and then bring it back up without it getting contaminated at other levels. In the film, there's a very high tech way of doing it where you have computer-controlled bottles. In earlier days, you had a bottle that went down on the end of a string, and you sent a little lead messenger down which opened the bottle to take a sample, and then a second messenger to close it again, and then you dragged it up. And you've got your sample from a known depth. And that's effectively what they're doing with the whole series of one litre bottles arranged in a circle and a computer deciding when to open and close the lids. And of course, it's very important to get the depth right because plankton do move up and down in the water. And this vertical migration of some plankton takes place on a daily basis. And then also, you get sudden increases in population at a particular point as a result of tidal movement. So for example, a population of phytoplankton might be swept past your equipment by the tide going one way and then swept back again going the other way. And this will produce, for example, a pulse in a detector that picks up phytoplankton, or it will produce a sudden surge in the number of individuals that were trapped in your bottle. INTERVIEWER We saw the painstaking work that was being done on the organism familiarly known as Tony by the research scientist. He said it had taken relentless hours of patience to come to some of the conclusions he's come to. Has it been groundbreaking, what he's produced, the research he's produced, about Tony? DR. DAVID ROBINSON I think the research that he's produced about Tony is extremely interesting, particularly because of where his sample comes from. And you can see in the clip the big drill bits and they're drilling down into the ground. What they're looking for is a lair of rock called an aquifer - that can be rock, sand, gravel - that is able to absorb a lot of water. And if that water becomes organically contaminated, then it will have bacteria in it. And Tony is living off the bacteria in that water. That is a very, very unusual place to look for life and to look for communities. Because, of course, Tony depends upon there being lots of bacteria there to feed on. And if the bacteria population declines, then populations of Tonys decline. And Tonys are able to form cysts, which can resist quite a bit of drying, as well as keeping the organism alive during a period when there aren't many bacteria about. And I think this is of course quite a common thing, of single-cell organisms forming cysts. But it's in this very strange environment, deep in water-bearing rock, I think makes it so special. Dr Gabrielle Kennaway is trying to find out more about planktonic organisms within their ecosystems and she is using very sophisticated equipment to sample the plankton. She refers to the equipment as a CDT, an instrument for measuring conductivity, temperature and depth that is equipped with sampling bottle. She is particularly searching for phytoplankton, microscopic plant life. She will show you how phytoplankton can be detected in the water and she reveals a very interesting event. Dr Paul Tett is interested in the behaviour of phytoplankton. He discusses the sources of energy in this aquatic ecosystem. Being small has advantages for phytoplankton and you should try and note the advantages that Dr Tett describes. Investigating phytoplankton NARRATOR Paul Tett is an ecologist who uses models from physics to shed light on the behaviour of oceanic plankton. PAUL TETT Understanding about the very small requires us to understand, first of all, the biology of the organisms, but also something about the physical nature of the environment in which they find themselves because we're dealing with a very different world at the level of the very small. The creatures that I'm studying are called plankton, and, in particular, the plant members of the plankton, the floating microscopic plants called phytoplankton. And you can see some of them there. These little plants are really microscopic, single cells. Each of them has some green chlorophyll and some red pigment. These colours are distinctive of different types of phytoplanktonic algae. So you would expect to find different coloured phytoplankton at different depths in the sea depending on the colour of the light that reaches them. They need light because they're plants. And they need light to grow. But in addition, they need things that I call nutrients, mineral nutrients. And these are salts or phosphates, and nitrate. The sort of thing that you'd find if you use Grow More fertiliser in the garden. The problem for phytoplankton is that they can very rarely get light and nutrients at the same time. Because light is at the surface of the sea and the nutrients are found deep down where organic matter decays in this cold water at the bottom of the sea. NARRATOR Being small does bring its compensations. PAUL TETT The advantages of being small, for phytoplankton, is that it helps them to get nutrients and it helps them to stay in the light. It helps them to get nutrients because a small creature has got a high ratio of surface area to volume. And it's the surface that governs the rate at which nutrient can be taken up. And it helps them to get light because small creatures sink very slowly in the sea water. And therefore, they can stay close to the surface of the sea. And the surface of the sea is where light is. NARRATOR These cultured phytoplankton are kept in the lab. They get optimal lighting and the ideal balance of nutrients. The sea is the dominant force in the life of the plankton. Their movement is dictated by motions of the water around them. Paul has modelled the forces that plankton experience. These vary from the smallest to the largest scale. PAUL TETT Plankton are carried around the ocean basins by currents. And one of the characteristic features of currents is that they form eddies and motions become irregular. And I can demonstrate that by pouring a little cream into my coffee cup. So first of all, I'll stir the coffee around to simulate the motion of water around the North Atlantic. And then I'll add the cream. And there it is forming swirls and eddies, which are characteristic of the largest scale of motion in the sea. On the smallest scale, the behaviour of water is dominated by the attraction between water molecules. This is called viscosity. It makes the water very sticky to small animals. It's as if they're living in honey rather than water. A consequence of the high viscosity at small scales is that microorganisms find it very difficult to get hold of particles from the water as perhaps will become apparent when I've buttered my toast and put some honey on it. Oh dear, and now, as is often the case, I've left a little smear of butter in the honey. So I better get that out. But it doesn't really want to come, does it? Let's try again. So for small organisms, it's as if they're wrapped in a jelly-like coat of this thick and viscous liquid. It's very hard for them to come into contact with other organisms or with their food. This is glycerine, a liquid which is much more viscous than water. And I'm using it to demonstrate the properties of water on the scale of small organisms. Now, what is remarkable about what I'll demonstrate is that I can reverse the effects of stirring in this liquid. You can't do that with water. When you've stirred your sugar into your teacup, you can't reassemble the sugar cube afterwards. So let's make this demonstration beginning by adding a few drops of this green glycerine. Now, I'm going to stir these drops. So as I go around, the drops elongate. And when I come back, they return, amazingly enough, to the original round shapes. There are strong implications of this for locomotion. Movement is completely reversible. A forward stroke, which drives the organism forward, is reversed by the backward stroke, which sucks the organism backwards. So these little creatures can't swim by moving their flagella up and down or forwards and backwards. Instead, they have to use a corkscrew like motion. 4.1.2 Investigating flagellates Dr Gianfranco Novarino is working on flagellates that occupy a very unusual ecosystem deep in the ground at Cape Cod, an organically contaminated aquifer – an underground water-bearing rock. It is, as he describes, a very basic ecosystem and probably one that you would not have thought of. Can you think why studying such ecosystems is important? Investigating flagellates NARRATOR Gianfranco Novarino specialises in a group of flagellates involved in the cleanup of organic pollution. GIANFRANCO NOVARINO A whale is made up of great many cells, a huge number of cells. And each cell is specialised in doing something very, very specific. Think about the poor amoeba or the poor flagellate. They are only made of one cell. And with that cell, they have to do everything that the whale does. So they are rather clever creatures. NARRATOR In order to reach these flagellates, you have to drill down deep. The cores are collected from Cape Cod Air Force Base in America and sent to Gianfranco's laboratory in London. GIANFRANCO NOVARINO The Cape Cod research started a few years ago. And it became immediately apparent that the dominant microbes inside the aquifer, apart from the bacteria, were flagellates, which occurred in only slightly lower numbers than the bacteria themselves. This was a fascinating ecosystem to study because it was very, very basic. We have bacteria breaking down organic substance and then we had the flagellates that were grazing on the bacteria. NARRATOR A new technique called RNA probing allows Gianfranco to estimate the number of flagellates in the sample. GIANFRANCO NOVARINO Conventional stains will stain DNA wherever it is contained. So it will stain every microbe in our preparation. On the other hand, by using the RNA probe, it is possible to stain only the organisms that we are really interested in. NARRATOR The flagellates stain yellow. The bacteria don't show up at all. The next step is to prepare new samples to isolate and identify the organisms they contain. GIANFRANCO NOVARINO The whole isolation process took a while. It was very exciting, even though it was a rather tedious job to isolate. And I think this really exemplifies very much of what research is all about. There's a lot of tedious, repetitive work, but if there is an underlying enthusiasm that motivates the researcher then that's really what research is all about. This is Tony, a totally undescribed flagellate from an organically contaminated aquifer that I've been studying for a number of years. It's about five micron in diameter, so pretty small. The reason why it has been named Tony is to honour Tony Manero, the star character of Saturday Night Fever in 1977. Tony Manero used to dance with one arm facing upwards and one facing downwards. And this is exactly how Tony swims. He can swim with one flagellum directed anteriorally and one directed posteriorally. Although, he can also use both flagella to project backwards. It's a beautiful organism. Obviously, this name will be changed to a proper scientific name, so a new name will be introduced in the literature. But it's very handy to have these off the cuff nicknames for new organisms that are awaiting formal description. What you can see here is another cell of Tony. It has slowed down in order to feed on these bacteria, in which you see a large number here in the background. And with a bit of luck we might just about be able to see the actual capture of a- ah, there it goes. Go back a bit. Watch this bacterium here. Now I can play that again. And it's gone. Nice catch for Tony. NARRATOR When there's plenty of food, the boom times, Tony shows another behaviour that's typical of microbes. GIANFRANCO NOVARINO Here you can see another cell of Tony. This cell has four flagella instead of two. The reason for that is that the flagella have replicated prior to cell division. What this cell will do eventually is divide into two daughter cells thanks to binary fission. In other words, when the bacterial populations in the aquifer are abundant there will be a population explosion of Tony. However, the story is very different when times are bad. When food is scarce cells of Tony produce a resistance stage, also called a cyst, which is a means to ensure long term population survival. The first thing that must be done is to settle down, come to a rest, and retract the flagella, as this cell is doing here. One flagellum has been retracted already. And the other one is in the course of being retracted. Eventually, this will produce a thick-walled resistance stage. We see a few cysts here, which is extremely resistant to heat, dessication, and of course, the absence of food. Activity 1 You now know something of the role of microscopic organisms in marine and aquatic ecosystems. What roles can you suggest that they might have in terrestrial ecosystems? Microscopic organisms have a variety of essential roles in terrestrial ecosystems. Examples you might have thought of include decomposing organic material, fixing nitrogen from the atmosphere and providing food for other organisms. Bacteria and other microorganisms are part of food chains in the soil. For example, important predators of soil microorganisms are nematode worms which are very tiny, about 1.0 mm in length. 4.1.3 Filtering food from the ocean As you learned earlier, the oceans are rich in nutrients in the form of very small and microscopic organisms. A whole range of animals make a living by filtering the small organisms from the surrounding water. Professor Mimi Köehl describes the problems that filter feeders have and helps you to visualise them. Filtering food from the ocean NARRATOR Creatures that feed on particles suspended in the water are a speciality for Mimi Koehl. PROFESSOR MIMI KOEHL Three quarters of the Earth's surface is covered with water. And that water is full of particles. And a vast array of different kinds of creatures make their living by filtering those particles out of the water. Some of them, like anchovies and whales, swim around and let the water move through their filters as they go. Other animals, like sea fans and feather duster worms and feather stars, sit on the bottom and put their filters up in the current and as the water blows through they capture particles. What all these different kinds of suspension feeders have in common is that their filters are all made up of a row of cylinders. And the water moves through the cylinders. So if we want to understand how all these diverse creatures catch their food, we need to understand how a row of cylinders catches particles. And one obvious way to catch particles is if a particle is bigger than the hole between the neighbouring cylinders, then as it's carried along in the flow it bangs into it and it's caught. We also know that organisms, in fact, catch particles that are much smaller than the gap between the cylinder, like this little model of particle might indicate. And that's a mystery. Here we've got cylinders, particles smaller than them, and you can see that they aren't caught. They aren't strained out. But what's different about my model and real organisms is that real organisms have sticky cylinders. And we can ask what happens to these small particles when they flow past sticky cylinders. And as you can see, particles are happily caught. And if you calculate the sizes of particles that are caught by any filter you discover that filter is a selective filter. It catches certain sizes of particles much more readily than other sizes. NARRATOR Inertia and viscosity are both important in the watery world of filter feeders. PROFESSOR MIMI KOEHL Now, there's a simple expression for how important inertia is relative to viscosity for any kind of flow situation. And that's the Reynolds number. When Reynolds number is high, what we have is a situation like us stirring the tea, where inertia dominates. And the flow is messy and turbulent. When we have low Reynolds number, it's a situation like us stirring the honey, where the viscosity is much bigger force than the inertia. Now, something to think about is the size of the organism that's stirring the fluid. When you and I stir tea, we're large. We displace a lot of water. And it has a lot of inertia. It keeps moving. If a copepod, which is the size of the flea, were in there stirring the tea, it's only displacing a tiny volume of water. And that little tiny volume doesn't have a lot of inertia. So the viscous forces in the water are bigger than the inertial forces for this little, tiny animal. NARRATOR For small creatures, water seems much more like honey. PROFESSOR MIMI KOEHL But let me show you a movie of a copepod with water moving past it. Now to see the water moving past it, what I did was just mix a little food colouring with some seawater. And I released that from a micro pipette near the copepod so we could see what the water looks like. And let's just run this movie and have a look at what that's like. And as you can see, this is just water, but it looks like honey. See how the dye stream sticks together? And even though the animal is flailing its appendages around, it doesn't get all mixed up and it's not turbulent like water flows around us. But this is water. Well, we can calculate what the Reynolds number would be for the second maxillae of different kinds of copepods. And what we find is some species operate at very low Reynolds numbers, as low as 10 to the minus 2. NARRATOR It's the Reynolds number that determines whether the second maxillae are leaky like sieves or act more like paddles. PROFESSOR MIMI KOEHL So let's start out looking at Centropages. This is an animal that operates its second maxillae at a Reynolds number of one. So we expect it to be leaky. It's in orientation with its head towards you and its second maxillae flapping like this. So they're going to be here on the picture. And we've marked some water with some food colouring. So let's watch what happens when the second maxillae sweep through some dye. Here's the animal. The second maxillae are folded up here. Here's the dye. And the second maxillae, bloop, did a flip through that. Now, let's watch it frame by frame. Here come the second maxillae flinging apart. This one's going to move right through this dye, so it's nice and leaky, just like we predicted. Now let's look at an animal that operates at Reynolds number 10 to the minus 2, Eucalanas. Again, it's in this orientation. Second maxillae are flapping here. Here, you can see the individual seeding of the second maxillae. Here's the dye. And look at this. As it flaps through the dye, it doesn't move through those gaps. And if we look frame by frame, here's the gaps. And as it sweeps through, you can see the dye doesn't move through. Even though there are holes there, they're functioning just like paddles. NARRATOR Whether they paddle or they leak, suspension feeders still manage to eat using different methods to achieve the same result. PROFESSOR MIMI KOEHL The animals that operate at Reynolds number one that are good and leaky, it's easy to imagine. They fling their second maxillae apart. When we squeeze them back together, the water squirts through those gaps between the hairs and they filter the particles just like you'd imagine. Now, let's look at an animal that operates at Reynolds number 10 to the minus 2. When the second maxillae fling apart, they draw a parcel of water towards the mouth of the animal. And the algal cell is carried with that water towards the mouth. And then they close over that parcel of water they caught. And they come in with some other appendages and they stuff that algal cell and the water into their mouth. So we have animals that are doing the same behaviour. They're flinging and squeezing the second maxillae. But the animals that operate at Reynolds number one are filterers. And the animals that operate at Reynolds number 10 to the minus 2 are catching those particles by moving the water around. So here we have Centropages. And you see her from the side. Here's is the second maxilla folded up over the animal's body. And these other appendages are flapping and creating a current of water past the animal. Now, when an algal cell approaches, whoop, you can see the second maxilla actually moves and catches this particle. So let's stop this and back it up and have another look at that, so we can see exactly what happens when the animal catches that particle. Now if we run it more slowly, what you can see is here comes the algal cell. And then the animal flings its second maxillae apart and squeezes them back together as it catches the particle. Activity 2 In Week 3 you learnt about size and shape in relation to animals and temperature. Now, think about the size and shape of organisms that live in a fluid medium. Give some examples of the particular problems that they encounter as a consequence of the physical properties of the fluid. Water is more viscous than air. It is also denser. For small organisms the water is very sticky, so because of their size it is like living in honey rather than water. Single cell organisms that swim using a whip-like strand called a flagellum can’t move by beating it backwards and forwards, but need to use a corkscrew motion, as described by Dr Tett in the video ‘Investigating phytoplankton' (Section 4.1.1). You might also have thought of problems of buoyancy. Fins that provide lift, such as those of sharks, counteract the tendency for the body to sink as it is denser than water. 4.2 Analysing ecosystems – a summary You have now looked at a range of ecosystems and the organisms that comprise them and it should be clear that you can study a system at a number of levels. At the top level is the flow of energy through the system. Sunlight drives photosynthesis and primary production, but also provides a source of heat energy that animals can utilise in raising body temperature or need to avoid in extreme habitats such as deserts. The links between organisms in an ecosystem are most obvious in food chains, so in addition to describing a system in terms of energy flow, you can describe it in terms of links between plant, animals, fungi or bacteria. The diversity of life in a particular system provides another level of analysis, where the physical properties of the habitats that make up the ecosystem have an influence on the adaptations that organisms have to survive there and the number of niches available. Some ecosystems encompass diversity hotspots, a term applied to Wicken Fen. In the next two weeks you will be considering the impact of humans on different ecosystems and you will appreciate that in order to understand and conserve you need to know what life forms are part of the system you are dealing with. In the next activity you will be exploring the identification of animals, plants and fungi and the ecological links between species. 4.3 Identifying organisms Identifying organisms inhabiting a particular ecosystem can be difficult. You are encouraged to do just that, using the iSpot website to help identification. Chris Packham introduces you to iSpot. Ecosystems and diversity - a practical activity CHRIS PACKHAM The Open University's iSpot is a great website. It's not only about phenology, noting seasonal markers. It's about general wildlife observations too and it's great fun. So, basically, if you are out and about and you come across something that's unusual in your area, or you can't identify, all you do is take a simple photograph of it - doesn't have to be a work of art - just a clear, concise photograph which you then upload to the site. Simply log-on to ispot.org.uk. It really is quick and easy to register. And once you've done it, you're ready to add your own exciting findings to the database and find out what everyone else is talking about. To upload a photo, just click on Add an Observation. Using the form provided, fill in as much information as you can about your find. The more specific you can be, the better. But if you're not sure what it is you've seen, just ask the iSpot community for their thoughts. You can even use the integrated map facility which allows you to pinpoint exactly where you took your photo. And that's all there is to it. Within a very short space of time, someone will have probably got back to you with an answer. This iSpot turned out to be a banded snail and within hours someone even deduced it might be a juvenile proving the site really does work. And it doesn't have to be just about identifying things either. If you see something that you're genuinely really excited about. Particularly if you're able to grab a picture and upload it. Then this is a great place to communicate your enthusiasm because the community that uses the site is there to do so. You'll get whole streams of people interacting about topics from all over the country. It's a place also - I've got to say - where you can learn a lot, as well. And the more people that sign up, get involved, and add their observations the better the site will become. It will slowly build up into an incredibly rich resource telling us lots of things about the wildlife in the UK. Some of which might help that wildlife in the future. So do everything you can to get involved. It's great fun. Discovering the species of organism that inhabits a particular ecosystem is obviously a crucial stage in working out the interactions that form the food chains and routes of energy flow in ecosystems. Identification can be difficult but there are online resources available to help. In this practical activity you are encouraged to go and look at animals, plants or fungi in a habitat that is easily accessible to you, photograph them if you can, and use the iSpot website to get help in identification. You will need to register with the iSpot website, but registration is free. Try and find four different organisms living in a habitat near you and suggest the place that they might occupy in an ecosystem. Ideally, for each you should take a photograph and upload it to iSpot. You will find instructions on how to do this in the iSpot guidance document. If you live in a region of the world where the climate is seasonal, you could look for organisms that are characteristic of the season of the year. The Great British Year poster covers the British seasons and suggests organisms to look out for each month. For any observation that you upload you can see if an interaction with another species has been recorded. You can also record an interaction that you have observed. For example, a photo of a butterfly might be linked to a particular food plant. Using the interaction feature on iSpot enables you to begin to construct links within an ecosystem. Be sure to tag your contribution as #oueco, so that you can connect with observations made by others on this course. Finally, contribute your observations to the discussion in the next step. 4.3.1 Ecosystems and diversity This is an opportunity for you to share the links to and discuss your four iSpot observations and your deductions about their links with other organisms. Go to the Week 4 forum and discuss the following questions: Are the four that you have observed linked to each other? Can you make any links to other people’s observations? 4.4 Week 4 quiz This quiz is about the smaller organisms at the base of food chains in simple and complex ecosystems. Complete the Week 4 quiz now. 4.5 Summary of Week 4 Dr David Robinson, Senior Lecturer in Biological Science at The Open University, discusses what you have learned so far and what's coming next. Summary of weeks 3 and 4 NARRATOR The examples of different environments around the world have raised questions about how organisms function within different ecosystems and explored how organisms and ecosystems function at microlevel. The next section explores another significant influencing factor on ecosystems. DR. DAVID ROBINSON Early humans were an integral part of the ecosystems in which they evolved. Modern humans range across the globe and have impacts on a wide variety of ecosystems to which they are not adapted. Sometimes, human intervention disrupts ecosystems that have been refined over long time periods on a short time scale that limits the ability of the system to respond. We have developed new ways of living, which can disrupt or destroy natural environments. But at the same time, our understanding of biology and nature is enabling us to make decisions which help to protect the natural environment. On the next part of this journey, you're going to face up to the effects that humans have on a variety of different ecosystems. Now, it isn't all bad news, but it pays us to take a long, hard look at human impacts if we are to minimise their disruptive potential. NARRATOR This section investigates how human activity affects the delicate energy balance in an ecosystem, often with adverse consequences. SPEAKER 1 In 1997, satellite data shows there's 1,116 million hectares of rainforest. That's a fall of 50% in just 22 years. And most of that loss is due to human activity. NARRATOR This video examines different challenges conservationists face from human activity around Wicken Fen in the UK. SPEAKER 2 Really, somewhere like Wicken Fen, at the moment, can almost be described as a paper handkerchief, a tiny little area now in a sea of different types of landscape. SPEAKER 3 Potential threats, like encroachment, could have a devastating impact on Wicken Fen because it is so small. Even contained disasters may wipe out a significant proportion of the reserve. NARRATOR This video investigates how locals and gorillas can inhabit the forest in harmony through the example of Bwindi Impenetrable National Park in Uganda. SPEAKER 4 For gorillas to have a sustainable future, local people needed to be involved in their conservation rather than excluded from the forest. SPEAKER 5 A question had come, say, oh, conserving for whom? And therefore, we had to make a shift from that fortress approach to an integrated conservation work mate approach. NARRATOR This video looks at the way that, as part of a restoration project, farmers were paid to keep their cattle off the hillsides of China's Loess Plateau. SPEAKER 6 What eventually convinced the local people was the assurance that they would have tenure of their land. That they would directly benefit from the effort they invested in the new project. NARRATOR This video examines three generations of a family in China who, since harvesting peanuts, have seen their income rise fourfold. SPEAKER 7 [SPEAKING CHINESE] DR. DAVID ROBINSON We humans occupy many different ecosystems and our impact is felt worldwide. We won't be able to conserve and restore everything, so with an understanding of ecosystems comes a responsibility to make hard decisions. In Weeks 3 and 4 we have considered ecosystems in three very different areas of the globe – deserts, the polar regions and the seas. Each area raised questions for you about how organisms function in different ecosystems and how they are adapted to the physical properties of their environment. You also learned about the need to identify organisms so that the nature of relationships within ecosystems can be evaluated. In the next two weeks you will examine the impact that humans have on ecosystems, using examples from around the world. If you would like a short break, or to find out more about studying with The Open University, take alook at our online prospectus. You can now go to Week 5. Week 5: Human impact Introduction How do humans affect ecosystems? Early humans were components of the ecosystem in which they evolved. Modern humans spread across a range of systems that differ from those in which the species originated. Ecosystems satisfy our needs for food, water and shelter, but unfortunately, human activities inevitably have an impact and may disrupt many ecosystems, some of them permanently. Human impacts may alter the interactions that take place within an ecosystem, or affect the productivity of the system – or both. Dr Mike Gillman and Dr Vince Gauci consider the consequences of human interference in well-balanced ecosystems. Humans enter the equation DR. MICHAEL GILLMAN Understanding ecosystems is all about understanding the interactions that are going on within each system. Looking at the types of interaction helps us to set up a system's boundaries. The transfer of energy and nutrients within the system helps us understand how it works. Key to this is measuring what happens to be energy that enters the system from the sun. The total energy trapped by photosynthesis in an ecosystem is called the gross primary production. The energy left after some has been used to maintain the plants themselves is called the net primary production. And that is key. The more net production an ecosystem has, the more energy there is available for transfer within the system. So what happens if the amount of net production changes? And what could make that happen? Yes, you guessed it. Like it or not, we have an impact on our environment and in turn, affect carefully balanced ecosystems around the world. Humans aren't the only factor, but it's worth looking at the effect we're having. In 1975, it was estimated there was approximately 2,450 million hectares of rainforest on the planet divided between Africa, Asia, and South America. In 1997, satellite data shows there's 1,116 million hectares of rainforest. That's a fall of 50% in just 22 years. And most of that loss is due to human activity. DR. VINCENT GAUCI The problem with unintended consequences are they're unintended and unforeseen. And while you could be manipulating a system like a rainforest by taking away the vegetation, what's quite clear is that you're removing habitat. What perhaps isn't so clear is that you can have knock on effects on its climate in the long term. DR. MICHAEL GILLMAN These knock on effects could be very small. But even tiny changes can be significant. Just how significant depends on what happens to the lost rainforest. Some ecosystems are more secure than others. They hold a better hand, as it were. But a few bad cards, and a rainforest system could quickly change. If the land is farmed, the ecosystem will change dramatically. When many trees are felled, rainforest can turn quickly into grassland. But even subtle influences over a longer time period can have a big effect. DR. VINCENT GAUCI If you have lots of species from an ecosystem, you really don't know what the effects will be. In some respects, we're going through a natural experiment right now where we're losing species. So by tracking what's going on in the Earth's ecosystems, we might be able to get a handle on this. An alternative approach is to actually set up our own experiments to investigate this question. DR. MICHAEL GILLMAN So humans do have an effect. And it can be significant. But it all depends on which part of the system is being affected by human activity. Take that most civilised of human activities - international air travel. Imagine that this luxury airliner is an ecosystem. For that first class experience, every bit of the plane is vital. But if we stopped serving free champagne, it would still fly. Take away the peanuts and the in flight movie, and it's still airborne. It'll even fly if one of its engines is on the blink. But there's a limit to how much we can remove before it all goes wrong. And we can think of ecosystems in exactly the same way. Some elements are crucial. But are there some additional extras the system could survive without? One system that's pretty much everything included is the system of pollination. But we could argue that we could do without the personal touch the bees provide. Many species are pollinated in other ways. And in truth, we don't know what would happen if we took bees out of the equation. Let's take another example - peat bogs. DR. VINCENT GAUCI If you start chipping away at an individual component of an ecosystem, you can have all sorts of unintended consequences. Now, one good example could be an upland peat bog. These humble ecosystems actually have been mined for years for their carbon. It's a form of fossil fuel. So in mining this apparently abiotic component of the system, there are consequences to that action, because this peat bog actually functions as a great big sponge. So when you have large rainfall events, that big sponge soaks up the rainfall, and it prevents that rainfall from disappearing down the rivers too fast. So you remove that sponge all of a sudden, you'll get flashier, more intense flooding events. DR. MICHAEL GILLMAN: So ecosystems are not fixed. They're carefully balanced, fragile, and subject to change, through natural disturbance and through human impact. 5.1 Managing or meddling Managing or meddling DR MICHAEL GILLMAN Ecosystems capture energy and recycle nutrients. They're delicately balanced and complex, living systems that are easily affected by external influences. They can be affected by human activity. But they can also be managed and operated as a kind of service provider. [PHONE RINGS] ACTOR Hello, Busy Bees, pollination section. Oh, yes, totally. Yeah, we cover all types of flower. DR MICHAEL GILLMAN It's estimated that as much as one third of human food supply depends on pollinators. ACTOR Definitely, definitely. We do an awful lot of work with lavender already, actually. DR MICHAEL GILLMAN The insects that do the pollinating could be natural, but they can also be artificially introduced into an ecosystem to help increase productivity. It's not really run by the Busy Bee Corporation, but it is big business. In the US alone in 2000, it was estimated to be worth $14.6 billion US dollars. But there are costs - maintaining the hives, transporting the bees. There's also the problem that the artificial honeybee may not be effective on all crops. We may have to look at the wild bees. One approach is to try and manage wild bees to make them more efficient pollinators. But another idea is to use the wild bees to influence the behaviour of the honeybees. We already know that meddling with an ecosystem can have side effects. But sometimes, these effects can work out for the best. DR VINCENT GAUCI Now you get all sorts of interactions between different species. And sometimes, you get unintended consequences of that. So it's not necessarily a negative. You can get positive interactions. Now, for example, with wild bees interacting with honeybees, it's actually been found that the net effect of that is actually even more pollination - overall a good thing in terms of what the system can provide us. DR MICHAEL GILLMAN Pollination is just one example of how we can manage ecosystems for our benefit. But as our man at the Busy Bee Corporation will tell you, it's not the only service that ecosystems can provide. ACTOR Indeed, we don't just do flowers. We also could do your woodlands, too. Oh, yes, that's why they call us the bees' knees. Heh. Yeah, mm. DR MICHAEL GILLMAN In some areas, the careful management of woodland could make a significant contribution to a local economy without destroying the system that's providing the wood. Coppicing is a good example. Yes, the trees are cut back, and yes, coppiced woods are man made, but there's a balance between harvest and maintenance. So their basic ecosystem remains intact. DR VINCENT GAUCI Ecosystems can be managed and make them sustainable and economically viable entities. There's active management of the wood to harvest, on an annual basis, part of the woody growth. This sustainable harvesting of the forest is actually to its overall benefit. And it's this sort of management of an ecosystem that actually can be a nice model for managing other types of ecosystem. DR MICHAEL GILLMAN So ecosystems can be manipulated to our economic advantage. But the key is careful management, because we don't always know what the ecological consequences of our actions will be. Ecosystems are complex, and so is our relationship with them. They provide us with food, water, and help protect our built environment. Yet, our activities have destroyed and altered many, allowing just a few to flourish. A better understanding of how ecosystems function will allow us to manage and sustain them for the future. Having a better understanding of how ecosystems function, and the energy flows through them, means that future damage and disruption can be limited. Here are some questions raised by this video and the previous one. Make brief notes on possible answers in preparation for the discussion at the end of this week. Can you think of examples where ecosystems have been negatively affected by human activity, and where they have been managed and operated to benefit humans without damage to the system? How does damage to one ecosystem have an impact on another? Why are small changes so significant? Do you agree with the following assessment: ‘Some elements [of ecosystems] are crucial but there are some additional extras the system could survive without.’ 5.2 Managing an ecosystem – the art of coppicing Professor David Streeter mentioned management of woodland by coppicing in an earlier video. Careful management of woodland can make a significant contribution to a local economy. Woodland that has been coppiced is a good example of a harvested, but sustainable, ecosystem. Watch this video in which Dr Janet Sumner shows how coppicing is done in managed woodland. Managing an ecosystem - the art of coppicing DR. JANET SUMNER Well, we've come back to Foxcombe Hall for our spring visit. And there are masses of jobs to do at this time of year. But one of the things we want to get stuck into is coppicing. Now coppicing is the process of cutting down trees and allowing them to regrow over a period of about 7 to 25 years. And it actually uses the natural regeneration cycle of many trees like oak, ash, willow, and in this case, hazel. Now the idea is is that you cut the tree down to a stump or stool, and it then re-grows with lots of smaller stems, rather than a single trunk. And to coppice, all you need is a saw and a little bit of expert guidance. Well, we're taking out some of these smaller poles to start with, to get into the bigger trunks. And then we're going to saw through those. And what we might do, actually, is count the rings on the trunk and see if we can work out the last time that this tree was coppiced. Now one of the things about when you're cutting down quite large trunks like this, is you definitely do need a hard hat on, and a pair of steel-toe capped boots. And you also need to be aware of which way the branch is going to fall. Now this one is leaning out, so it's going to go that way. So I'm fine where I'm standing. But for heaven's sake, also check that there's nobody else in the vicinity that it could fall on. Now each one of these rings in the tree represents a year of growth. They're annual growth rings. So if I count them up, theoretically, that should tell me the last time this tree was coppiced. I'm just looking through here, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30. I got something like 30, 33, 35 rings through here. It's not that easy to see. So we're looking at a stump here, or a trunk that's about 35 years old. And of course, the rings, as well, can be an indication of climate change. And also show when the tree had a good year, and when the tree had a bad year. Now coppicing isn't all about just simply cutting the trunks down. There's quite an art to it. You need to cut them quite close to the thickest part of the trunk at about 30 to 45 degrees facing outwards, away from the stump, so that the rainwater will drain off and away from the stump core, which prevents the stump from rotting. Now we've just got here in time, actually. Because if you look at some of these smaller branches, they're absolutely soaking. And that's the sap rising up through the tree. So we just need to finish this one off with a few more cuts. Now when you coppice, what you get, apart from a lovely, neat stump, is a lot of these. Beautiful, long, straight stems, which are variously called stems or poles, depending on the thickness of them. Now coppicing is a practice that has gone on for generations, hundreds of years. And these poles have been used for all sorts of things, from making coracles to wattle and daub in Tudor houses. And you can see they're beautifully straight. They make great handles for tools, and, broomsticks, and things like that. But they're also used as firewood and charcoal. The uses are really endless. They're beautifully flexible, as well. So, yeah, hopefully we'll get lots of these poles growing out of this stump. 5.3 The survival of Wicken Fen We will now revisit Wicken Fen, Britain’s oldest nature reserve. The reserve is being managed artificially, in order to support multiple habitats, and by extension multiple species and multiple food chains. Those working on the reserve believe that without management the fen would be overtaken by bushes and trees, which would reduce the number of habitats, and support fewer species. Survival of Wicken Fen NARRATOR Succession is an ongoing natural process. If humans didn't manage the fen, succession would continue, and much of the land here would be covered with bushes and trees. This would greatly reduce the diversity of habitats available, and therefore, the diversity of species. Management of succession is a key reason why biodiversity of this fen is so high. JOANNA FREELAND Management is important at Wicken Fen, because it, in effect, halts the progression of succession at different stages. If there wasn't any management, succession would just continue through to the, what's termed the climax, which, in most places in the UK, is forests. ADRIAN CALSTON And what we're trying to do at Wicken is hold those different areas of succession so that we can have the whole range of the different habitats, from the open water through the meadows through the sedge fields and also the areas of scrub. And by doing that, that really enables us to have the maximum diversity on the site. NARRATOR The sedge harvest is another of the key management tools used on the fen. By cutting the fen's sedge fields on a regular basis, succession is halted before trees and bushes can grow. This type of management is very intensive. It requires a considerable amount of time and labour. Maintaining the fen solely through such intensive methods is unrealistic. The cost alone makes it prohibitive. So the management committee at Wicken is also using other ways of halting succession. Large herbivores, like cattle, have been used for many years. Using grazing animals like these provides a cost effective and environmentally friendly way of maintaining open fen. More recently, a herd of wild ponies has been brought to Wicken. CAROL LAIDLAW The area, before the ponies were introduced, was covered by large trees and scrub, small bushes. We've done quite a lot of work manually cutting the trees down to try and revert the land. The ponies are here to keep on top of the work we've already previously done. And as they move through an area, obviously that will have an impact. So we should see quite a mosaic of habitats - sedge fields punctuated with grass meadows, reed fields, again, punctuated with sedge. NARRATOR Grazers represent a more sustainable way of managing the existing fen. But even management techniques like this may not be enough to guarantee its long term future. One of the main threats to the fen is its situation in the middle of farmland. Unlike the fen itself, the surrounding farms have been drained so that crops can be grown. Drainage effectively shrinks the soil. This means the fen now stands at a higher level than the neighbouring land. MARTIN LESTER The site is perched somewhere in the region of two to three metres or more above the surrounding farmland, which means that when you're trying to manage a wetland in those sort of conditions, water is very difficult to keep in. You can't stack it up with the best will in the world, which has meant that much of the site is actually now surrounded with a waterproof membrane to keep the water in. So hydrology is a big problem for us. NARRATOR Maintaining water levels is not the only problem the site is faced with. MARTIN LESTER Wicken is fairly close to a number of small villages. But it's also quite close to Cambridge, Ely, and Newmarket. And potentially, that number of people close on the doorstep could be a problem. NARRATOR Potential threats like encroachment could have a devastating impact on Wicken Fen. Because it is so small, even contained disasters may wipe out a significant proportion of the reserve, in the process, eliminating habitats and species. ADRIAN CALSTON Really, somewhere like Wicken Fen at the moment can almost be described as a paper handkerchief, a tiny little area now in a sea of different types of landscape i.e. a very agricultural landscape. If we're going to try and maintain the species that we've got here, we really need to try and expand the fen and give greater scale for these species to actually live on so they can move out and spread and have a better chance of survival in the future. And as a result of that, the National Trust has drawn up this vision relief for Wicken Fen for the next 100 years. And it involves acquiring land around the fen, gradually restoring that back to some form of wetlands. And we hope to, over the next 100 years, create that much larger area which will act as the buffer for the fen, new habitats for wildlife. NARRATOR This increase in scale means the reserve can support larger populations of species within a diversity of habitats. And these larger populations are less likely to go extinct. On the other hand, if the area of Wicken Fen isn't increased, it will be less likely to survive in the long term, seriously depleting biodiversity levels in the UK, JOANNA FREELAND The significance of Wicken Fen is that it's one of the very few areas of fenland remaining in the UK. And it's home to a huge diversity of species, many of which can be found only in this type of fenland. If we lost a place like Wicken Fen, we would lose a huge number of species along with it. And the UK as a whole does not have a huge amount of biodiversity. And to lose a place as important as this would put a real dent in all of the UK's biodiversity. ADRIAN CALSTON If Wicken Fen was lost tomorrow, we would certainly see 7,000 species disappear from this part of the world. A number of those species are now incredibly rare in the UK, maybe one or two other sites. So we would see some species almost being pushed to extinction in the UK. And what we would also see, I think, with the loss of Wicken, is the failure of conservation. And if we fail at Wicken, it's really only time, then, before we fail everywhere else. NARRATOR High levels of species diversity rely on several factors - a range of habitats, the preservation of food webs, and in the case of Wicken, management of the fen. The National Trust plan to increase the size of the nature reserve at Wicken accommodates all these factors and will increase the chances that the fens unique biodiversity will survive. Is this a case where human intervention is a positive factor acting on the ecosystems present? Would you consider the fen to be an artificial ecosystem – one that would not exist but for human intervention? Here are some questions raised by this video. Make brief notes on possible answers in preparation for the discussion later. What are the factors contributing to high level of species diversity? What is the significance of Wicken Fen? What kind of ecosystems and habitats would result if Wicken Fen wasn’t managed by humans? Does the need for biodiversity outweigh the need for natural succession? What kind of management tools are used to managed Wicken Fen? What would be the result if Wicken Fen was destroyed or lost? Contributors to this video include David Gowing (OU), Joanna Freeland (OU), Adrian Calston (Property Manager, Wicken Fen), Carol Laidlaw (Warden, Wicken Fen), Martin Lester (Head Warden, Wicken Fen). 5.4 Conserving a rare species The fen-raft spider (Dolomedes plantarius) was only discovered in the UK in 1956. It is very rare and its distribution prior to 1956 is not known. This throws up some interesting questions about a re-introduction programme, since the habitats into which spiders are released may – or may not – have originally had the spider in. Think about the implications, before watching the next video and learning more about the re-introduction programme. Habitat restoration and managed re-introduction are two techniques that are key to conserving individual species. The fen-raft spider is an endangered species, as Dr Helen Smith and Chris Sperring explain in the video. Conserving a fen species INTERVIEWER Well, what a glorious autumn day here in the county of Suffolk. I'm actually on the open marshland of the Suffolk Wildlife Trust nature reserve of Carlton Marshes. And I'm actually here for a spider. And the person that's going to introduce me to these spiders is Helen Smith. Helen, what is it you're actually doing? HELEN SMITH Well, today, we are putting out some tiny fen raft spiders on the ditches on this reserve to start to set up a new population. This is one of Britain's rarest, biggest, most beautiful spiders. It occurs in only three places in the wild in the UK. And we're just starting work on Natural England's programme of introducing it to new sites to try and secure its population in this country for the future. INTERVIEWER So did this area, Helen, did it ever have fen raft spiders in big numbers? HELEN SMITH Well, we don't know the answer to that. We're never going to know the answer to that. They weren't discovered in the UK until 1956. I think we just have to make some sensible assumptions based on the current distribution, which is here in Suffolk, down in Sussex, and across in Wales; and a species that relies on clean, lowland wetlands. And we know what's happened to the majority of our clean, lowland wetlands. So I think it's almost inevitable that we've lost the species from large areas of Britain. INTERVIEWER Why choose this particular site, not any other site around? What's particularly good about this site for them? HELEN SMITH This site is part of the Suffolk Trust's move to try and connect back together a lot of its wetland nature reserves along the lower Waveney, creating huge areas for wildlife. And so introducing spiders here, and we're also introducing them to another site a bit upstream, is a first step, stepping stones if you like, to start to create a much bigger joined-up population and utilise that big network that the Trust are creating. But we've been working towards the translocation programme, really, for the last five years, very much starting to look at what sites would be suitable and actually how to achieve it in practice. INTERVIEWER Have you actually released before? Is this the first of the releases? HELEN SMITH No, we started last year. We released at a site just upstream from here. And just in the last few months, we've been starting to see the spiderlings looking fabulous out there on the water soldier over there, stripes gleaming in the sun. INTERVIEWER So a real success? HELEN SMITH Yeah, very-- INTERVIEWER A real success-- HELEN SMITH --every time we see one there. INTERVIEWER --especially after the winter we had. HELEN SMITH Yeah, no, it's just so exciting every time see one, particularly when we find a new ditch with one on. They look so at home. INTERVIEWER Well, Helen, you've just got out of the tub a full adult live raft spider. What a beautiful specimen. HELEN SMITH Yeah, she's fabulous. INTERVIEWER She's very dominantly, kind of, like a muddy brown, isn't she? Sort of like an estuary brown-- HELEN SMITH Yes. INTERVIEWER --with these two very distinctive bands going around either side of the abdomen? HELEN SMITH --and the thorax. INTERVIEWER --and the thorax. HELEN SMITH Yeah, sort of like "go faster" stripes, really. They're sort of goldie-colored now. But often, in the younger spiders, they're brilliant white on a black background. INTERVIEWER What's the difference between the male and the female? HELEN SMITH Well, nothing really until they're sort of penultimate moult when they become sub-adult. And then suddenly, the male starts to acquire clubbed ends to his palps, which become the insemination organ in the adult. INTERVIEWER Is it true they go underwater as well? HELEN SMITH Yeah, absolutely. They spend quite a bit of time underwater. So sometimes it's an escape response from predators. So while I'm monitoring them on Redgrave and Lopham Fen, I get in the water and work with them there. And some spiders will go straight underwater as soon as I get in. But you can often see them there because the hairs on their body trap air, and so they look glistening silver underwater. But they also hunt underwater. So they'll catch sticklebacks and water boatmen underwater. INTERVIEWER So this is the adult. Now, what about the young ones? HELEN SMITH The young ones look exactly the same, just brighter and miniature. INTERVIEWER Now, we can hear you rattling around there. What you're actually carrying, what looks like, well, it's a plastic tray. And inside that plastic tray, it looks like hundreds of test tubes. HELEN SMITH Well, it is hundreds of test tubes. We've got about 600 tiny spiders to put out here today. These are basically the babies of spiders taken from Redgrave and Lopham Fen in June, with the egg sacs. So they hatch their egg sacs. We potted up the spiderlings into individual tubes to stop them cannibalising each other. And they're being fed in those tubes, so we can get very, very high survival rates that way. So we've bred something like 2,500 baby spiders this year. So that's me working with lovely collaboration with several UK zoos. And the other really big contributors are volunteers who make a huge difference to this project, some that's really carried me through some dark days of this project. INTERVIEWER So how do you actually rear a spiderling? HELEN SMITH Well, it's quite easy really. I mean, once they're about a week old, which is the stage where they'd normally leave their nursery, they go into the test tube with damp cotton wool in the bottom. And we have to get fruit flies in there for them on a very regular basis. INTERVIEWER So they really do spend their early life in these tubes. HELEN SMITH Yeah, they do. INTERVIEWER They're not just being transported today? HELEN SMITH Yes INTERVIEWER So Helen's got a group of test tubes in her hand there. And she's checking them over very thoroughly, I must add. Helen, why are you checking them out thoroughly? HELEN SMITH Well, I want to be quite sure that nobody's in the process of changing their skin because they usually attach themselves to the lid. And just before, during, and just after skin changing, they are very vulnerable because they're so soft. And things can go wrong if you disturb them at that stage. But this lot look fine. And you can just see the little shed skins in there from the last time they did it. You can actually see the white stripes on the shed skins. INTERVIEWER Yeah. HELEN SMITH So the tubes are strung together with lines of masking tape. And I do it that way so that they're well-spaced out as they leave the tubes, rather than ending up in the heap where-- INTERVIEWER So Helen's undoing the top of the test tubes. I'm looking inside one of these tubes at the moment. And they really are tiny spiders. You can actually see a brown back on one of those, almost like a rusty brown back. HELEN SMITH Off you go. INTERVIEWER One's come out, lowering itself down on the thread into the vegetation. And it's off into its new world. HELEN SMITH It's quite nerve-wracking, the whole process, I find, you know, introducing something to a site where it probably hasn't been for a very long time. And however carefully you follow the guidelines for translocation, and we certainly do, there's always that bit of unknown out there. INTERVIEWER But that's good, isn't it? HELEN SMITH We can never be quite sure. INTERVIEWER You care. You don't just care, I can really hear you're passionate about these spiders. HELEN SMITH Well, they've lived with me for a long time. You get to like that about them. I am passionate about seeing their population restored in the wild. INTERVIEWER So these spiderlings now, we can see that they're making their way out quite slowly, and then lowering themselves from the tubes down into vegetation by their threads. How do they actually live on the water? How do they do it? HELEN SMITH At this stage, they actually spend very little time on the water. But by the spring, they will be out sitting along the water's edge. They're usually seen sitting where stems emerge from the water, often with their back legs on vegetation and their front legs on the meniscus. And they have specialised hairs in their legs and their feet. And they can detect tiny vibrations in the water surface which tell them where their prey are and where their predators are. So they're very tuned in with this sort of vibratory sensory system to living on water. And they use that system for courtship as well. So the courtship is very much based around creating vibrations on the water surface. INTERVIEWER Now, why do you release at this time of the year? HELEN SMITH Well, two reasons really. You can see these very, very tiny animals, lots of things will predate them at this stage; although as adults, they become very fierce predators themselves. But this stage, they're very vulnerable. And we know from the size of our wild populations, we can get over 90% survival rearing in this way. So we are skipping an enormous amount of the mortality that would happen in the wild. INTERVIEWER So they're being released now, what happens next? HELEN SMITH Well, the ones that don't get eaten will hibernate during the winter. And I have to say we know remarkably little about what they do in the winter. It's like looking for needles in haystacks. They're almost certainly in air spaces in hollow plant stems. Some of them could be in air spaces underwater. If you look at the Pevensey marshes in early spring, before the water soldiers come up, you see very few fen raft spiders. And a month later, they're absolutely everywhere. So once these ones, which hatched this summer, will spend next summer growing, they'll become sub-adult. Their penultimate skin change next autumn. And then the following spring, they'll mature into adults and breed during that summer and die at the end of it. INTERVIEWER So we're not just talking about the release of these. There's some quite intricate monitoring going on as well, isn't there? HELEN SMITH Yes, very much so. So we're monitoring both the populations of the new spiders, and something very much that volunteers are helping with increasingly, which is very valuable. And we're also doing genetic monitoring of the new population. So we're looking at what's going out and, genetically, what of that we retain over time. INTERVIEWER Presumably when you're doing that work as well, you're finding out that you haven't got a subspecies. HELEN SMITH Yes, no evidence at all of any barriers to breeding. We looked at breeding. And we looked at mating behaviour, courtship behaviour. We looked at survival of the young. We looked at the number of offspring produced. And actually next year, we're going to look at the F2, the next generation as well, just to be doubly sure. INTERVIEWER Is there a problem releasing another predator, another spider predator within an environment like this? HELEN SMITH It's very difficult to give you a very definitive answer to that. But I think the best answer is that the places where these spiders occur in the wild now are three of our richest wetlands - very, very high diversity. And these spiders clearly fit into that ecosystem. They have a place there. They would have been there in the past. INTERVIEWER This area here looks very similar to the area I come from, which is the Somerset Levels. What's the chances, Helen, of me having a few spiderlings to take back? HELEN SMITH One thing that we're going to be doing in the next few years is looking for additional sites for reintroductions. The action plan for this species suggests 12 sites in the UK by 2020. We're currently looking at six sites now. We're certainly going to start to look at some of the inland fens because of concerns that these broadland sites are going to be gradually salinised as sea levels rise. INTERVIEWER How long the monitoring go on for? HELEN SMITH I think monitoring needs to go on almost indefinitely for species as rare as this. These are animals which are so rare, they should be being monitored on a very regular basis. The action plan for this species has a 2020 target. If we're going to achieve that target, I think the programme will have to go on probably until 2020, but the monitoring very much longer. And the habitat here has been through bad patches in the post-war years. A lot of these fields have agriculturally improved. The ditches became eutrophic. And now, as you can see, they're being beautifully restored by the Trust. And so to have one of the species that have been lost back here, I think it's just very appropriate. INTERVIEWER : So we're not only talking about - earlier, we were talking about joined-up habitats, the fact that there's more habitats going to be created that are like this, we're also talking about joined-up spiders. HELEN SMITH Yes, joined-up spiders. And I think that it adds enormous point to the translocation. I think if we were introducing to a few more tiny isolated sites, I would see that as having much less future and being much less worthwhile than being able to bring them somewhere like this, where we know that if they do well, they can move out through these ditch networks over a huge area of the Norfolk Broads eventually. Activity 1 What is the significance of joined-up habitats in a conservation programme? Connecting back together a lot of habitats can create huge areas for wildlife. So introducing species at one site, and other nearby sites, is like laying stepping stones to start to create a much bigger joined-up population and to utilise a larger network. In highly developed countries land becomes fragmented so corridors that link conservation areas are crucial to maintaining diversity. If the climate changes, such corridors can provide migration routes to, for example, cooler habitats. You can find out more about the fen raft spider online. 5.5 Week 5 quiz This quiz is about the human impact on ecosystems and the effects of ecosystem management. Complete the Week 5 quiz now. 5.6 Human influences on ecosystems Here are some of the questions that you have been considering this week. Can you think of examples where ecosystems have been negatively affected by human activity, and where they have been managed and operated to benefit humans without damage to the system? How does damage to one ecosystem have an impact on another? Why are small changes so significant? Do you agree with the following assessment: ‘Some elements [of ecosystems] are crucial but there are some additional extras the system could survive without.’ What are the factors contributing to high level of species diversity and does the need for biodiversity outweigh the need for natural succession? What is the significance of Wicken Fen? What kind of ecosystems and habitats would result if it wasn’t managed by humans? What would be the result if Wicken Fen was destroyed or lost? As you consider the questions, you might like to explore the topics covered this week in the Ecosystems area on OpenLearn. Use your answers to these questions to discuss the advantages and disadvantages of management of ecosystems in the Week 5 forum. You will continue to explore the impact of humans on the environment in Week 6. Week 6: Fragile ecosystems Introduction We bring the last five weeks together, looking at issues of large scale management and conservation, concluding with a study of the Galápagos archipelago World Heritage Site. 6.1 Gorillas and tourism Bwindi Impenetrable National Park in Uganda was formed in an attempt to protect the jungle in the area, one of Africa’s richest ecosystems, from human activities. Initially it was preserved in a hostile way, with local residents forcibly evicted and barred from future entry into the park. This sparked angry protest from local communities, and there were violent clashes as a result. An integrated conservation development programme was conceived to protect the area without alienating local communities, who had been dependent on the resources available in the forests and jungle for their livelihood. Gorillas and tourism DR. GLADYS KALEMA-ZIKUSOKA The gorillas are very important. And mountain gorillas are one of our closest living relatives. We share 98.4% genetic material. And when you go out to see them, it's very therapeutic. They look into the eye. And you feel like you're connecting with a close relative. There's only over 700 gorillas left in the world. NARRATOR Mountain gorillas are one of the world's most endangered species, teetering on the edge of extinction for decades. Today, they survive only in the forests of Central Africa, where they have endured years of civil war, habitat loss, and poaching for bush meat. TUGUMISIRIZE YESE We used to see the gorillas. There were very few, but those few, people never feared killing them. They are vermin like other vermin. They were killed. They were poached. There was no problem NARRATOR Half of the world's remaining population of mountain gorillas is found here, in Bwindi Impenetrable National Park in Uganda. But as the park lies in the heart of one of the most densely populated parts of Africa, it's continually under threat from people eager to use the forest's rich resources. CHARITY BWIZA The population pressure is increasing. And the population in southwestern Uganda is the highest in Uganda. And it is also said it is the highest in Africa. But the land is not increasing. NARRATOR To deal with this threat, the Fortress Conservation approach was adopted in Bwindi. This aimed for the total exclusion of people and their activities from the forest, enforced by armed rangers. JAMES BYAMUKAMA Originally the communities were allowed to access a number of resources. They would access firewood. They would get mushrooms. They would get wild meat. They would get bamboo shoots - bamboo and many hand craft products. And when it was made a national park, then these rights were removed. The removal of any of the forest's products was stopped. And this implied that the communities lost all what they would get as contribution to their livelihood. And therefore, the communities came out in rage. CHARITY BWIZA Communities used to set fire intentionally to the protected area. Then communities used to fight with the law enforcement. So the communities were really, really very hostile. NARRATOR As conservation by force wasn't working, a new approach was needed. This conflict had to be resolved. For gorillas to have a sustainable future, local people needed to be involved in their conservation rather than excluded from the forest. JAMES BYAMUKAMA A question had come - conserving for who? Therefore, we had to make a shift from that fortress approach to an integrated conservation and development approach and put the people into conservation. NARRATOR The integrated conservation and development approach works by linking wildlife conservation with the welfare of the people around the park. MOSES MAPESA We had to review and rethink the strategy to look into to how to make these conservation areas more relevant to the people who live close to them or who even have ancestral claims to the land. And that is how the whole notion of integrated conservation and development programmes started. ALASTAIR MCNEILAGE One initiative designed to reduce the conflict was also what we call the multiple use programme. The idea was to take account of the fact that, actually, some of the things that people want from the forest - small amounts of medicinal plants, weaving materials - could actually be harvested without having a major impact on the forest itself. The quantities they need may be quite small. The resources may be plants which grow quite quickly and are easily renewed. And allowing the communities to access those resources could be used as a strategy to give them something back MAN Wild yams help us live longer and remain resistant to diseases. That’s the main reason we like them. WOMAN I gather enough material to weave three baskets, and I keep one to use in the home and sell two. MAN When the forest was closed there were problems, but since, we’ve been able to access things we need. We’ve collaborated with the park officials and there have been no problems. TUGUMISIRIZE YESE Some non-government organisations, even the government, have tried to improve the nature of the people neighbouring that gorilla so that they shouldn't at any time point a finger at the gorilla. NARRATOR Communities were helped to develop a new livelihood activities to replace those lost from their restricted access to the park. CHARITY BWIZA We are finding different variances of community projects, like bee keeping and like mushroom growing. People used to go into the park to harvest wild mushroom, so we started funding individuals and groups to grow mushrooms. TUGUMISIRIZE YESE They give me the materials - the sterilising drums, the drier. After helping me with such, then they give me knowledge, enough knowledge to grow mushrooms. NARRATOR Now, conservation was actually benefiting the local communities, and their view of gorillas and the forest began to change. TUGUMISIRIZE YESE Do I need to go to the park to look for mushrooms to supply the hotels? The mushrooms are here. Contributors to this video include G. Kalema-Zikusoka, T. Yese, C. Bwiza, J. Byamukama, M. Mapesa. The crucial point of the development programme was to involve communities in the increased tourist interest in the park and its gorilla population. As you watch the next film, reflect on why the Bwindi Park was established, and how this affected the local population. What difference has the establishment of the park made to the ecosystems there? Consider whether the economic activities around the park make enough of a difference to the local communities around the park Gorillas and tourists ALASTAIR MCNEILAGE At the same time, another organisation was starting up, a gorilla tourism programme trying to find ways that the forest could generate income sustainably without being harvested, without being cut down, without killing animals. So that that provided income both to pay for the management of the park itself, pay for all the salaries of the rangers and the guides and the park staff and the maintenance of the forest, but also to generate income for the local communities. FEMALE TOURIST It's amazing. You never see anything like this. NARRATOR Now, gorilla tourism is seen as the answer to conservation. It's based on the simple economic principle that there is more money to be made from tourist dollars than from selling of natural resources. MOSES MAPESA We stopped timber companies or timber harvesting in Bwindi, and we earn a lot more money from the great apes tourism, from the gorilla tourism, than we would ever earn from timber production. TUGUMISIRIZE YESE We respect the gorilla because of tourism. It's a bigger income to our country. And what's also very wonderful about the gorilla tourism beginning is that the local communities' perceptions of conservation have changed significantly because they now see the gorillas as a sustainable source of income for them. NARRATOR Revenue from tourism trickles down to communities via job creation and extra trade, but there is also a scheme that puts a percentage of park entrance fees directly into the hands of local people. ENOCK TURYAGYENDA You know, there is some little money, which normally comes in the parishes every year. We call it revenue sharing. That money comes from UWA. It is the money, which these whites normally contribute to visit to this park to help the citizens who live around the park. GHAD KANYANGYEYO In the beginning, everything like wildlife to me it was useless, because there was nothing I was benefiting from them. Many local people were just taking anything as if it was nothing. And then they would chop the trees down. It would kill the animals and all, but now things have changed. Everybody is now putting pressure on conservation because we are benefiting from more life. Everybody is benefiting from tourism. NARRATOR Any long term plan needed to be profitable and offer sustainable livelihoods to local communities. Gorilla tourism has done this with some surprising results. In 2006, a census found a total of 340 gorillas in the park, an astonishing 12% increase in the population over the preceding decade. MOSES MAPESA We can begin to talk about a very positive trend in the conservation of Bwindi and the gorillas specifically. We have seen a steady rise in the gorilla population, and habitat is still large enough to accommodate a few more gorilla families. NARRATOR But is the integrated conservation and development approach supported by the money from tourism really sustainable? Is it the answer to saving the gorillas? ALASTAIR MCNEILAGE What doesn't always work as well, which perhaps is a bit unrealistic, is to think that through these ICD projects, you're going to improve people's livelihoods so much. I mean, you're talking about maybe helping people to move from being very poor to poor, but they're still poor. And so just because they may be able to cultivate more crops and raise some goats doesn't mean to say that they still don't have great needs, which could still be met by getting resources from the park. JAMES BYAMUKAMA You cannot be in charge of the minds of the people. The needs of the people keep changing day by day. And they are quite many people around here, for example, who still feel, even if you give them alternatives or substitutes for bushmeat, who still feel that bushmeat is what they need. What do we do with them? We still have to get back into the forest to trap. So I think Fortress Conservation and integrated conservation development approaches have to be combined. And the kind of management that brings about that is what we call adaptive management. You adapt the management according to the situation. Join the Week 6 forum and discuss the problems faced by the Bwindi Inpenetrable National Park in conserving their population of gorillas. Are there any general conclusions that can be drawn from the gorillas that can be applied to the conservation of other species? 6.2 China’s Loess Plateau China’s Loess Plateau is a region that stretches for 640,000 square kilometres across north central China. It is an example of an ecosystem that has been ravaged by human activities, such as agriculture. China’s Loess Plateau JOHN D LIU This is China's Loess Plateau. Until recently, this was one of the poorest regions in the country, a land renowned for floods, mud slides, and famine. But with the fanfare comes the hope of change for the better. My name is John D. Liu. I've been documenting the changes on the plateau for 15 years. I first came here in 1995 to film an ambitious project where local people were constructing a new landscape on a vast scale, transforming a barren land into a green and fertile one. The project certainly changed my life, convincing me to become a soil scientist. The lessons I've learned in the last few years have made me realise that many of the human tragedies that we regularly witness around the world - the floods, mud slides, droughts, and famines - are not inevitable. Here on the Loess Plateau, I've witnessed that people can lift themselves out of poverty. They can radically improve their environment, and by doing so, reduce the threat of climate change. When I first came to the Loess Plateau, I was astounded by the degree of poverty and degradation. And I wondered, how could the Chinese people, the largest ethnic group on the planet, and my father's and my own ancestors, come from a place that was this barren? China's Loess Plateau is a region that stretches for 640,000 square kilometres across North Central China. Unspoiled valleys in neighbouring Sichuan show us how it might once have looked. It's the sort of natural abundance that is necessary to support an emerging civilisation. How could a landscape with such potential have been reduced to this? When Chinese scientists and civil engineers began to survey the area, they realised that several thousand years of agricultural exploitation had denuded the hills and valleys of vegetation. The relentless grazing of domestic animals on the slopes meant that there was no chance for young trees and shrubs to grow. The rainfall no longer seeped into the earth, but simply washed down the hillsides, taking the soil with it. Over millennia, this progressively destroyed the region's fertility. When this happens over an area as extensive as the Plateau, millions of tonnes of silt are swept down into the Yellow River, which gets its name from the colour of the fine Loess soil. The mounting quantities of silt clog up the river, impeding its flow, contributing to the floods that give the river another name, China's Sorrow. In some areas, creating floating mud mattresses that attract passing tourists. A local problem becomes a national problem. In the dry season, the light, unprotected soil is swept up in the winds, causing the dust storms that are blown over China's cities and beyond its borders. On the Plateau, the researchers realised that progressive degradation of the environment trapped the local population into a life of subsistence farming. It's a process that has occurred throughout the world, where poor agricultural communities find themselves overusing their land in order to survive, depleting its fertility, and further impoverishing themselves. One thing that became apparent early on is the connection between damaged environments and human poverty. In many parts of the world, there's been a vicious cycle. Continuous use of the land has led to subsistence agriculture. And generation by generation, this has further degraded the soils. The vital question we have to ask is, can this destructive process be reversed? 15 years ago, Chinese and international experts were confident it could be. They decided that to prevent further erosion, it was necessary to cease farming on certain key areas to allow the trees and shrubs to grow back. But this could not happen without the consent of the farmers themselves. They took some persuading. MR. TAFUYUAN [SPEAKING FOREIGN LANGUAGE] TRANSLATOR: Of course, a lot of people didn't understand the project. They weren't thinking in the long term. VILLAGER [SPEAKING FOREIGN LANGUAGE] TRANSLATOR They want us to plant trees everywhere. Even in the good land. What about the next generation? They can't eat trees. JOHN D LIU What eventually convinced the local people was the assurance that they would have tenure of their land, that they would directly benefit from the effort they invested in the new project. MR. TAFUYUAN [SPEAKING FOREIGN LANGUAGE] TRANSLATOR The goal was to give a hat to the hilltops, give a belt to the hills, as well as shoes at the base. The hats meant that the top of these hills had to be replanted with trees. The belt meant that terraces had to be built, to be used for crop planting and also for trees. The shoes were the dams, which we had to build so that the hills could grow back to life, and our economy as well as our lives could improve. JOHN D LIU Hills and gullies were designated as ecological zones to be protected. Farmers were given financial compensation for not farming on them and keeping their livestock penned up. When I first filmed Mr. Tafuyuan and his colleagues back in 1995, I had no idea this initiative could achieve such dramatic results. The effort that people put into converting their slopes into terraces has resulted in a marked increase in agricultural productivity. The higher yields are directly related to the return of natural vegetation and the surrounding ecological land. Now when it rains, the water no longer runs straight off the slopes. Trapped by the vegetation, it sinks into the ground, where it is retained in the soil, taking weeks and months to gently seep down and irrigate the fields and terraces below. Restoration has occurred over an area of 35,000 square kilometres. The impact of such an enormous addition of vegetation goes far beyond the plateau itself. There's been a significant reduction in the soil rushing down into the Yellow River. As I've been travelling around the Loess Plateau, I've seen extensive changes. The vegetation cover on the hillsides, on the tops of the hills, and down in the valley, everything has changed. It's changed the lives of the people. And in fact, the people themselves have done this because they were the ones who changed their behaviours, terraced the fields, improved the soils, learned to protect the marginal areas. The changes are not simply on the hillsides. On the plains, you can see greenhouses that are filled with vegetables. This extends the growing season. It's very high value produce. The abundance and variety of new produce can be seen in the local markets. Follow up studies have shown that incomes have risen threefold. And scientists point to a more global benefit. Plants, through photosynthesis, remove carbon from the air, countering the effect of human greenhouse gas emissions on the climate. PROF. CAI MANTANG [SPEAKING FOREIGN LANGUAGE] TRANSLATOR In terms of climate change, we can say that the project made a double contribution. Firstly, the project was successful in restoring vegetation on a large scale. So many trees and so much vegetation grew up, and this definitely helped take carbon out of the atmosphere. Secondly, because the health of the Loess Plateau's ecosystem has been so much improved, the region will be better able to resist the negative impacts of climate change. JOHN D LIU As a result of its success, the lessons learned from the Loess Plateau rehabilitation are now being applied all over China. But could such projects work elsewhere in less centrally controlled societies with fewer resources and different soils? Contributors to this video include John D Liu. Video: ©co-produced by The Open University and EEMP for BBC World, with support from the International Union for the Conservation of Nature (IUCN), The Open University, The Rockefeller Foundation, and the Syngenta Foundation for Sustainable Agriculture and The World Bank. © Environmental Educational Media Project (EEMP) 2009 The hills and valleys of China’s Loess Plateau eroded because grazing domestic animals denuded them of vegetation. Valuable soil was washed away into the nearby Yellow River, leaving the plateau unfertile. The rehabilitation of the plateau has been a slow and arduous task. As you watch the next video think about the following questions: What were the activities that resulted in the destruction of the Loess Plateau? What actions were taken to restore the plateau? Loess Plateau’s success SPEAKER I remember when I was a kid, the water would run terribly off the slopes. Now that the trees have grown this doesn’t happen any more. Before the soil was very poor. It was difficult to grown anything on it. The land we used to cultivate was large, but it produced little. Now we have less land, but it produces more. So things have improved. In the beginning, I didn’t think much of the project. I was only a few years old, so I didn’t think that much. I was a bit afraid. VILLAGER 1 Now we eat noodles and rice. Life has improved. Before, the best we had was millet. When conditions were bad, we did not even have millet. VILLAGER 2 Before we hardly had anything to eat or wear. Life was really difficult. It’s much better now. Now we eat well and dress better. Conditions have really improved. SPEAKER Our standard of living has clearly increased. Our revenues are much higher than before. Now everything is much greener than before. It’s much better. Before everything was so barren, there was nothing. Now, it’s green. Video: ©co-produced by The Open University and EEMP for BBC World, with support from the International Union for the Conservation of Nature (IUCN), The Open University, The Rockefeller Foundation, and the Syngenta Foundation for Sustainable Agriculture and The World Bank. © Environmental Educational Media Project (EEMP) 2009 Activity 1 How can the destruction and rehabilitation of the Loess Plateau be understood in terms of an ecosystem? Write some notes in the box below. The Loess Plateau can be considered as a discrete ecosystem. As it became over-exploited the flow of energy through the food chains within the ecosystem changed and reduced. Unless the primary flow of energy from sunlight into plant material for consumers is maintained, the ecosystem will change in character and, as in the case of the Loess Plateau, parts can become almost barren. Several thousand years of human agriculture denuded the hills and valleys of vegetation. Domestic animals fed on vegetation and there was no chance for young trees and shrubs to grow. Rain no longer seeped into the ground but washed down the sides of the hills carrying away soil. Thus the primary route for energy to enter the ecosystem disappeared. 6.3 Galápagos The Galápagos archipelago is a unique ecosystem with a diverse collection of island habitats. It is a World Heritage Site and many of the plant and animal species are found nowhere else. The islands also have historical significance in the development of biological science, following the visit by Charles Darwin in 1835. The islands had a profound influence on his ideas about species formation, which culminated in his book On the origin of species by means of natural selection (1857). The islands have been the focus of scientific research for many years, but the conservation problems are substantial. This week the course will feature a series of video portraits about the archipelago. This series of portraits of the islands highlights the biodiversity found there, the problems of invasive species, the value of the islands for research and the problems of maintaining a flourishing ecosystem. As you watch the videos, think about these questions and take notes that will help you to answer them. Bearing in mind the definition of an ecosystem that you encountered at the start of this journey, is it reasonable to regard the whole archipelago as an ecosystem? What tensions arise between keeping the islands pristine, allowing visitors and allowing colonisation from the mainland? What major threats to the integrity of the habitats on Galápagos can you identify? Are they peculiar to the islands or applicable to ecosystems in general? 6.3.1 Darwin’s arrival on the Galápagos Islands Although it is possible to follow in Darwin’s footsteps, as Dr David Robinson demonstrates in this video, the habitat has changed substantially as a consequence of the introduction of alien animals in the past. There are very few of the larger islands where you can see ecosystems unaffected by alien introductions and thus see them as Darwin saw them. Darwin’s arrival on the Galápagos Islands DR. DAVID ROBINSON On the 8th of October, 1835, the survey ship, HMS Beagle, anchored in this bay. On board was Charles Darwin. And he and four companions were put ashore on this island for a week - an island that he described as both picturesque and curious. In Darwin's day it was called James Island. Today it's known as Santiago. At almost 600 square kilometres, it's one of the larger islands in the Galapagos. Its highest point is 900 metres above sea level. On Santiago, Darwin met two Spaniards who were hard at work butchering tortoises for their meat. Together, they had an uncomfortable walk across this lava field. Eventually they arrived at this volcanic lake where the Spaniards collected salt to use as a preservative. Darwin was fascinated by local flora and fauna. He described the Galápagos as a world within itself - full of creatures that were both curious and remarkable. The islands were teeming with wildlife. There were so many land iguanas, for instance, that Darwin found it difficult to pitch his tent without covering their burrows. Today, there are none left on Santiago. In total, Darwin spent five weeks on the Galápagos - experimenting, observing, and collecting specimens. As for tortoise meat, he noted that it tasted particularly good when roasted in its shell. The finches that Darwin brought back from the Galápagos hold a special place in the history of the development of the theory of evolution by means of natural selection. There are 13 species and they occupy different niches in the habitats on the islands. Finches on Galápagos DR. DAVID ROBINSON Although he didn't realise it at the time, the most important specimens that Charles Darwin brought back from the Galápagos were finches. Initially, he wasn't sure how they were related. But when back in England, they were examined by the ornithologist John Gould, he reported that, in fact, Darwin had brought back 13 different species of finch all of which were unique to the Galápagos. This realisation played a significant role in Darwin's formulation of his theory of evolution. The most important differences between the finches came in their beaks. Some were large, some were small. Each one was suited to the availability of particular foodstuffs. Eventually, Darwin theorised that different species of finch had evolved on different islands, their distinctive beaks being an adaptation to distinct natural habitats or environmental niches. In the years since Darwin's visit, many other scientists and ornithologists have come to the Galápagos to study its finches. In this experiment, researchers are observing the woodpecker finch using this wooden box to stand in for a tree. The woodpecker finch is one of the only birds to use tools to help it find food. A stick or small twig enables it to dig deeper into tree bark for insect larvae. This skill enables it to survive in conditions which other birds would find difficult. In the dry season, it can gather up to 50% of its food in this way. Woodpecker finches are hungry birds, which in the wild need to eat every three hours, so they never turn down the chance of a free meal. 6.3.2 Darwin’s thoughts on the iguanas The marine iguanas of the Galápagos are the only marine lizards and occur nowhere else. They occupy a fragile ecosystem that is very vulnerable to changes in sea temperature. There is also a species of land iguana on the islands. Darwin’s thoughts on the iguanas DR. DAVID ROBINSON Some of the most remarkable creatures encountered by Darwin on the Galápagos were its iguanas. He was particularly fascinated by the marine variety though he was far from flattering. Darwin wrote that they were hideous-looking creatures of a dirty black colour, stupid, and sluggish in their movements. He did concede, however, that they were strong, graceful swimmers. Bearing in mind how much time they spent in the water, Darwin was surprised to find that marine iguanas didn't eat fish. He dissected several creatures and found that their stomachs were full of seaweed. Darwin noticed that the water was too cold for marine iguanas to stay in for a long time. When they weren't feeding, he observed them clinging to the rocks above the shoreline, basking in the sun. After the cold sea, these reptiles craved warmth. Darwin was also interested in their terrestrial cousins, although again, he wasn't very complimentary about their appearance. He called them small, ugly animals with a singularly stupid appearance and lazy, half-torpid movements. Today they're still plentiful on some islands. But marine iguanas are particularly vulnerable to changes in sea temperature, which can have a dramatic effect on the availability of seaweed. Activity 2 Why, do you think, is the marine iguana so vulnerable to sea temperature changes? What impacts of environmental change might make the land iguana vulnerable? The marine iguana feeds exclusively on a small number of species of seaweed. The seaweed needs relatively cool water and in some years, when the ocean currents reverse, the seas around the islands get too warm for the seaweed and it dies back. The marine iguanas then have no food and die in large numbers. Any prolonged warming of the seas would make the species highly vulnerable to extinction. Land iguanas get most of their water from prickly pear cacti and the rest from rain fall. Any prolonged period without rain due to changes in climate put land iguanas at risk. 6.3.2 Invasive alien species The tortoises that gave the Galápagos islands their name are now threatened by alien introductions. Goats have been a particular problem, but slowly the populations have been brought under control. The habitat, the wariness of goats and remoteness of the islands make eradicating goats a very expensive proposition. Goats compete with tortoises DR. DAVID ROBINSON When Darwin visited the Galápagos, almost every island was crowded with wildlife. Most large islands had their own species of tortoise, which could be identified by the distinctive shape of its shell. Today, some of these species are extinct, and on some islands, the tortoises are limited to nature reserves. The problem is people. Settlers to the islands have brought in farm animals and other nonnative species, which have had a devastating effect on native habitats. The tortoises, which gave the Galápagos Islands their name, have found themselves sharing their food with wild goats, the descendants of animals brought into the Galápagos by Ecuadorian fisherman and British pirates. The tortoises don't have the same reach as the goats. They're happy with handouts in the tortoise sanctuary, but find it harder to compete in the wild. On the island of Isabela, for example, at one stage, the goat population reached a staggering 50,000, and the national park authorities had to begin an eradication programme. MICHAEL BLIEMSRIEDER Eradication programme, in this case, means just get out and shoot these goats either by foot or by helicopter, or who knows, but we have to kill them so the vegetation can have a chance to recover. DR. DAVID ROBINSON By 2002, Isabela was cleared of its goat problem, and scientists were cautiously optimistic that the tortoises might be able to reclaim their territory. Like the animals on the Galápagos, much of the flora of the islands is also vulnerable to the impacts of introduced alien species. In recent years around 500 species have been introduced. Amongst the most devastating has been the red quinine tree. Eradicating the red quinine plant DR. DAVID ROBINSON The Galápagos are famous for their reptiles and birds. But much of the islands' flora is equally interesting, and it's just as vulnerable to the impact of humans. Over the last centuries, almost 500 species of plant have been imported into the Galápagos, some for agriculture, some for gardens, and some by accident. Like the wild goats who compete with indigenous tortoises for food, so these newcomers compete with local plants for sunlight, soil, and water. Santa Cruz, for example, is home to a unique species of plant called Miconia, which is only found on one other island. Today, it is under threat from the red quinine tree, first brought onto the islands in the late 1940s. The red quinine tree is very hardy, and it reproduces so rapidly that there were worries that it might wipe out the whole of the Miconia zone. Today, the National Park Service are actively engaged in a programme to eradicate the red quinine; injecting any seed-bearing trees with cartridges filled with herbicide. It's expensive, time-consuming work, and there are many trees to kill. But scientists are optimistic that they may eventually eradicate the most damaging newcomers. 6.3.3 Galápagos research and human effects Most of the animals and birds on the islands have no fear of humans, which is one of a number of reasons why the islands are such an attractive place to carry out research. Galápagos research DR. DAVID ROBINSON We're in the Pacific, about 1000 kilometres west of South America on the equator. Martin Wikelski is heading for his research site. It's an island called Santa Fe, part of the Galápagos archipelago. Santa Fe, like all the Galápagos Islands, is the tip of a volcano that became land only a few million years ago. Many of the animals and plants that now live there are found nowhere else on Earth. These island species have long fascinated biologists interested in evolution, but this is also a good place for animal physiologists to study. Like all animals found in isolated oceanic island groups, the species found in Galápagos are astonishingly unafraid of people because of the absence of predators. And even on an inhabited island on a hotel patio, marine iguanas, a Galápagos species, lounge in the shade of the chairs. With few natural predators, they don't see people as a threat. They're easy to observe and study, and a source of fascination. This video highlights the pressures of increasing tourism and increasing population. Since the video was made, an area of land close to Puerto Ayora, the main town on Santa Cruz, has been set aside for 1200 new houses, which will double the size of the town. Managing tourism in the Galápagos Islands DR. DAVID ROBINSON When Charles Darwin landed on the Galápagos Islands in 1835, they were barely inhabited. But today things are very different. Over the last quarter century, the permanent population has grown rapidly from 5,000 in 1980 to over 25,000 today. This has caused problems for the National Park Service who want to preserve the unique character of the islands. MICHAEL BLIEMSRIEDER An increasing population size is a problem. For example, here in Santa Cruz and Puerta Ayora where we are now, there's no more space. The last areas were given away already to immigrants during the last four or five months, so people is living already at the borderline of the park. DR. DAVID ROBINSON In addition to the local population, over 150,000 tourists visit the Galápagos every year. The numbers keep on growing. Tourism on the Galápagos is tightly controlled by the Park Service. Some islands are totally closed off. Wardens supervise visitors at all times within the park zone, but there's such interest in these islands that the tourists keep on coming. CHANTAL BLANTON I think Galápagos should be important as a tourist area because one of the major purposes of protection in Galápagos is for conservation and for education. And it's very difficult for people to understand the problems that occur in Galápagos or in protected areas such as if they can't actually come here and see it with their own eyes. The problem from tourism isn't so much the tourist interaction with the organisms. What is more of a concern is all the people that tourism, as an ancillary activity, bring to the islands. And that is a concern because the islands cannot support large numbers of people. DR. DAVID ROBINSON So far, the Park Service and its supporters have managed to keep the big hotel chains and the huge cruise ships at bay. But the competing pressures of maintaining the islands' unique heritage and simultaneously allowing the local population to develop economically will always require delicate handling. Life on the Galápagos can be difficult, but nevertheless, scientists and conservationists regard it as a privilege to work there. MICHAEL BLIEMSRIEDER There are plenty of problems, and plenty of difficult situations, and plenty of frustrations, but they're also plenty of rewards and success. And things you can say, well, I helped to do this. I am getting an ulcer and things like that. I'm getting sick sometimes because of the problems, but well, that's part of the job. I mean, I prefer to be here instead of sitting at a desk at the main office in Quito. CHANTAL BLANTON Number one here is conservation. Number one here is this continuum to be, not a museum, not a vivarium. It's a living laboratory of evolution. DR. DAVID ROBINSON In the decades since Darwin's visit, the fame of the Galápagos has spread around the world. Much more is known about its natural history, but there's still much work to be done. Darwin's comment still holds true. It really is a remarkable and curious place. 6.3.4 A fragile ecosystem Before you started watching this week’s videos about the Galápagos you were asked to consider three questions. You should now be able to answers them and set them in the context of your overall study of ecosystems. Activity 3 Answer the questions in the box below. Bearing in mind the definition of an ecosystem that you encountered at the start of this journey, is it reasonable to regard the whole archipelago as an ecosystem? What tensions arise between keeping the islands pristine, allowing visitors and allowing colonisation from the mainland? What major threats to the integrity of the habitats on Galápagos can you identify? Are they peculiar to the islands or applicable to ecosystems in general? The islands are probably best regarded as individual ecosystems but the marine environment around the islands might be considered as a single, separate, ecosystem. As you learnt earlier, the physical boundaries of an ecosystem are influenced by the definition that you adopt and it would be possible to argue that for a definition in terms of energy flow, the whole archipelago is a single ecosystem. Keeping the remaining pristine islands in pristine condition can be done by not allowing access, but it is difficult to prevent humans landing on islands and patrols to keep intruders at bay would themselves compromise the pristine nature of the islands. Another factor to consider is the money that visitors bring. Would they be so keen to contribute money if they couldn’t visit? The threats to the integrity of the habitats fall into three broad categories. Human activity and population growth is an obvious one that effects the islands and it is a global factor. Alien introductions of plants and animals have wrought havoc in the past and can do so in the future. They are a risk to all ecosystems but the Galápagos are particularly vulnerable. Finally, global climate changes or volcanic activity could change the habitats on the islands. 6.4 End of course quiz This is a longer quiz so you can check your understanding of the whole course. Take the end of course quiz now. 6.5 Conclusion Dr David Robinson, Lead Educator and Senior Lecturer in Biological Science at The Open University, discusses and summarises the contents of this course, and the skills and knowledge you will have gained from it. Your journey has taken you to a variety of places, from Wicken Fen in Britain to the Bwindi Impenetrable National Park in Africa; from the Loess Plateau in China to the Pacific Islands of the Galápagos. These places have shown you a variety of different ecosystems, but there are two common themes: conservation and restoration. Neither of these activities can be undertaken without a very clear understanding of the ecosystems themselves. At the start of this course three over-arching questions were posed. You should now be able to answer those questions. ‘What is the importance of understanding ecosystems, how do they work and how crucial is their conservation?’ Conclusion DR. DAVID ROBINSON The natural world has been a continuing fascination for me throughout my professional life. And when I was a student, my ecology notes started with a quotation. "Ecological research of the most basic kind is vital to solving our environmental problems." And that's still very apposite today. Ecology, the scientific study of ecosystems, will be hugely important for the 21st century. Your journey has taken you to a variety of places, from Wicken Fen in Britain, to Africa to the Bwindi National Park, to the lowest plateau in China and finally, the Pacific Islands of the Galápagos. These places have shown you a variety of different ecosystems, but there are two common themes, conservation and restoration. Now, neither of these activities can be undertaken without a very clear understanding of the ecosystems themselves. You'll now appreciate the complex and beautiful relationships between the organisms in these ecosystems. The Galápagos Islands illustrate only too well how fragile ecosystems are. One change, such as the introduction of the alien red quinine tree can totally alter relationships within an ecosystem and hence, the whole system itself. Some events, like this one, are a result of human activities, but natural events can also potentially produce big changes. Every few years in Galápagos, the cool ocean currents from the south reverse and warm water from the north bathes the islands. The seaweed that the marine iguanas eat does not thrive in warm water and the plants die back. The result, no food for the iguanas and they die in large numbers. A prolonged reversal of the ocean currents might wipe out all the iguana populations. You might like to think about how this would affect the ecosystem as a whole. Unless we understand the links between species, we cannot limit damage, conserve, or restore, which emphasises that the study of ecosystems is a core part of biological science. This brings us back to the question that I posed for you at the start of your journey. What is the importance of understanding ecosystems, what they're comprised of, and how they work? Well, now you can answer that question. 6.6 Beyond ecosystems Well done for completing Introduction to ecosystems. If you have studied the full course and completed all the quizzes you will receive a Statement of Participation certificate as a record of your achievement. You can access and print it from your MyOpenLearn profile. If you would like to learn more about natural history in general, here are some possibilities: Explore OpenLearn further: Ecosystems: Taking it further Woodlands – in our Neighbourhood Nature unit Polar regions – using our Frozen Planet interactive The Galápagos World Heritage Site – by listening to our podcasts Continue your membership of the iSpot community and contribute your observations at www.ispotnature.org/. Contribute to the UK national map of trees at treezilla. Good luck with your learning. Now you've completed the course we would again appreciate a few minutes of your time to tell us a bit about your experience of studying it and what you plan to do next. We will use this information to provide better online experiences for all our learners and to share our findings with others. If you’d like to help, please fill in this optional survey Except for third party materials and otherwise stated in the acknowledgements section, this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence. The material acknowledged below is Proprietary and used under licence (not subject to Creative Commons Licence). Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: Week 1 Figures Figure 1 © Shawndra Hayes-Budgen (Scorpions and Centaurs)/Flickr.com Figure 2 © The Open University Figure 3 © cinoby/iStockphoto.com Week 1 AV The wetlands of Wicken Fen © The Open University, contains BBC clips © BBC Week 2 Figures Figure 1 © fotoVoyager/iStockphoto.com Figure 2 © sborisov/iStockphoto.com Figure 3 ©keiichihiki/iStockphoto.com Figure 4 © Dr David J Robinson FRES Figure 5 © sakakawea7/iStockphoto.com Figure 6 © Valmol48/iStockphoto.com Figure 7 © Dorling_Kindersley/iStockphoto.com Figure 8 © Smithore/iStockphoto.com Week 2 AV Introduction video © The Open University, contains BBC clips © BBC Following a food chain © The Open University, contains BBC clips ©BBC How plants make food © The Open University, contains BBC clips ©BBC Life in trees: squirrels © BBC Watching flying foxes © The Open University/BBC Week 3 Figures Figure 1 © Ron_Thomas/iStockphoto.com Figure 2 © Dr David J Robinson FRES Figure 3 © Mlenny/iStockphoto.com Figure 4 © The Open University Figure 5 © ColbyJoe/iStockphoto.com Figure 6 © Robinson, M., A Field Guide to Frogs of Australia Figure 7 © The Open University Figure 8 © Dr Peter Davies Figure 9 © Brad Alexander Figure 12 © The Open University Figure 13 © Dr Lloyd Glenn Ingles, California Academy of Sciences Figure 14 © The Open University Figure 15 © Dr David J Robinson FRES Figure 16 © zanskar/iStockphoto.com Figure 17 © (a) DmitryND/iStockphoto.com (b) Dr Angelika Renner Figure 18 © Dr David J Robinson FRES Figure 19 © Dr David J Robinson FRES Week 3 AV Krill © Video: British Antarctic Survey, Text: The Open University Large scale change © Video: British Antarctic Survey, Text: The Open University Week 4 Figures Figure 1 © Dr David J Robinson Figure 2 © micro_photo/iStockphoto.com Figure 3 © micro_photo/iStockphoto.com Figure 4 © The Open University Figure 5 © Dr David J Robinson Figure 6 © Dr David J Robinson Week 4 AV Filtering food from the ocean © The Open University, contains BBC clips ©BBC Ecosystems and diversity - a practical activity © The Open University/BBC Week 5 Figures Figure 1 © Dr Patricia J Ash Figure 2 © Chris Sperring/BBC Figure 3 © photocabin/iStockphoto.com Week 6 Figures Figure 1 © kemo1980/iStockphoto.com Figure 2 © guenterguni/iStockphoto.com Figure 3 © Dr David J Robinson FRES Figure 4 © Dr David J Robinson FRES Figure 5 © da-kuk/iStockphoto.com Week 6 AV China’s Loess Plateau © Text: The Open University Loess Plateau’s success © Text: The Open University Conclusion © The Open University Every effort has been made to contact copyright owners. 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