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Studying mammals: Chisellers
Studying mammals: Chisellers

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1 The rodent

As you work through this course you will come across boxes, like this one, which give you advice about the study skills that you will be developing as you progress through the course. To avoid breaking up the flow of the text, they will usually appear at the start or end of the sections.

As well as the course text, you will be using The Life of Mammals book (LoM) and related The Life of Mammals DVDs, as described in the introduction to this course. Before you go any further, watch 'Chisellers' on the DVD and read LoM Chapter 3. Unless stated otherwise, all the page references you encounter in this course will be to LoM.

At the start of LoM Chapter 3 you are immediately introduced to the importance of teeth for this group of animals. The 'chisellers' have the equipment to eat a very wide range of plant material, including leaves, bark, roots and seeds, and sometimes (as with beavers) wood itself. And as with other groups, their teeth are not used just for eating. They enable some members of the group to construct elaborate residences (the beaver's lodges, the mole-rat's underground caverns) and they can be used for fighting, as you can see on p. 78 in the photograph of two naked mole-rats squaring up to do battle.

All of the animals described in LoM Chapter 3 are members of the mammalian order Rodentia. The rodents are widely regarded as amongst the most successful of all the mammalian groups. They can be considered successful in terms of the number of species, comprising over 40% of all mammal species; most estimates nowadays are of the order of 2000 rodent species, and as the TV programme 'Chisellers' states, more than half (1300 by David Attenborough's (DA's) estimate) are loosely termed 'mouse-like rodents'. Rodents are also successful in terms of productivity: a single female Norwegian rat could have 56 young and over 400 grandchildren within 20 weeks of being born. And despite the fact that many of the photographs in LoM are delightful, this mammalian group is the one that many people would readily admit to disliking. Our dislike is perhaps partly rooted in the destruction that they wreak within our communities. It is estimated that 20% of the world's total food supply is either consumed or contaminated by rodents. Their role as carriers of pestilence, affecting both human societies and their livestock, has been understood and feared for many generations. It has been claimed that rat-borne typhus has single-handedly been responsible for more deaths than all the wars and revolutions throughout the history of humankind. But the war we wage against rats is singularly unsuccessful (they are notoriously difficult to poison) so it behoves us to learn more about this group, if only to enable our attempts to control them to be more effective.

In this course, I will examine some features of rodent biology that contribute to their success, in particular their exploitation of a unique range of plant foods, especially seeds, wood and roots. Seeds are rich in energy, but many roots and wood are tough and not very nutritious. Many seed eaters do not have to spend huge periods of time gathering their food, and so have time to spend ses001on other useful behaviours, such as reproduction. Whilst focusing on rodent feeding behaviour I will also be exploring some more general ideas concerning the origin of the features that make an important contribution to rodent success. To do so I will need to introduce you to important biological principles relating to evolutionary biology: natural selection and reproductive strategies.