3 Ecology: some background information

3.1 Habitat

The environment in which any organism lives is known as its habitat. It will share its habitat with other organisms, that are themselves part of the habitat. A habitat has distinctive physical and chemical features.

Question 4

Can you give any examples, from general knowledge, of the physical and chemical features of your habitat?

Answer

Obviously this depends on where you live, but you might have noted conditions of temperature and rainfall. You will be aware of hilly, undulating or flat surroundings. The quality of the underlying terrain may be less obvious, but if you have travelled around a little you may have noticed trees and shrubs that are common in some areas are rare in others. If you are a gardener, you might have attributed this to factors such as the soil quality, being familiar with the concept that plants have quite narrow tolerances. For example, some plants such as camellias are unable to thrive on a chalky, lime-rich soil (such a soil is described as mildly alkaline and has a high pH value) whereas others, like wild thyme, cannot grow in a peaty soil (very acidic with a low pH value).

An example of a food chain involving Eucalyptus and the koala. Note that koala are totally dependent on Eucalyptus.
Figure 1 An example of a food chain involving Eucalyptus and the koala. Note that koala are totally dependent on Eucalyptus. They do not eat any other plant.

Habitats can be quite varied, even over relatively small distances. A pond, wood and meadow all provide different habitats, but even so, some organisms may move between habitats (perhaps at different times of the year). For example, a bird might feed on seeds from early-flowering woodland plants and later progress to grass seeds from the meadow. When organisms have very precise habitat requirements, the loss of that aspect of the environment has serious consequences. It is well known that koala must have a diet of leaves from certain species of Eucalyptus, and given the importance of the koala to the Australian tourist industry we might expect that every care will be taken to ensure that their dietary needs are met. The relationship between these two organisms can be expressed as a food chain (see Figure 1). In a food chain plants are described as primary producers. Plants are eaten by herbivores, termed primary consumers; in their turn these animals may be eaten by carnivores, who will be secondary consumers. Although it is slow-moving, an adult koala weighs around 101kg and has strong claws so lacks natural predators. However, koalas were driven close to extinction in the early part of the 20th century because people killed them for their skin (rather than their flesh). They will just as surely become extinct if we destroy their food source. Nor is this a remote possibility. But Australians are now more aware of the ecological implications of clearing the bush for urban development.