Anti-Predator Behaviour

Abstract

In the last chapter we discussed some of the problems facing a hungry animal as it searches for food. Finding food, however, is only one side of a two-sided coin. Apart from finding its own food, an animal must avoid becoming food itself. As we emphasise several times in this book, an animal’s behaviour is usually a compromise between several conflicting selection pressures. The degree to which an animal adapts to one pressure depends on how that adaptation affects the other activities it has to perform. If a particular selection pressure is intense, then we might expect adaptation to proceed a good way towards reducing it before the utility of adaptation in that direction is outweighed by other selection pressures. For most animals, predation constitutes one of the severest everyday pressures. It is not surprising, therefore, that many possess extreme morphological, physiological or behavioural adaptations to reduce their risk of predation. As Harvey and Greenwood¹³⁵ point out, however, it is important to emphasise that predation need not be a limiting factor in a prey population for a genetically based anti-predator strategy to evolve. Like the hypothetical herbivorous insect example in the last chapter, any mutant individual who is just a little better at avoiding predation is likely to have a higher inclusive fitness than its conspecifics. The mutant will therefore spread even though it does not necessarily facilitate an increase in population size and density. In addition, anti-predator mechanisms may evolve for the protection of individuals other than the one possessing the mechanism.