Protean defence by prey animals.

Attention is drawn to the widespread occurrence ofprotean phenomena, in which the appearance and behaviour of prey animals are rendered variable and irregular, as a weapon in the biological arms race between predators and their prey. Protean behaviour is defined as that behaviour which is sufficiently unsystematic to prevent a reactor predicting in detail the position or actions of the actor.Single prey animals frequently flee from a predator in an irregular manner, zigzagging, spinning, looping, or bouncing. Thissingle erratic display occurs widely in the Animal Kingdom, and may also be utilised in everyday movements of potential prey as insurance against possible attack. Examples are given.In a group of prey animals the protean aspect of escape is enhanced by the effect of numbers. In scatter reactions the effect is of multiple choice and of the simultaneous operation of several single erratics. In mobbing displays there are also successive changes in the actors' behavioural role. In protean deterrence the shuffling of individuals within a tightly packed group prevents a predator from singling one out for attack.In many species the confusing effect of changes in movement and behavioural role is enhanced by rapid changes in appearance, particularly colour.It is suggested that those prey individuals which employ escape patterns unfamiliar to the predator will tend to be at a selective advantage. During phylogeny this is likely to lead to intra-specific and inter-specific increase in the number and diversity of escape behaviours. Apostatic polymorphism is seen as a special case of protean variation within populations.There is evidence that protean displays operate by arousing neurological conflict, thereby delaying the predator's reactions and reducing the effectiveness of predatory mechanisms. Also they insure against learned countermeasures by incorporating irregularities as a basic principle. It is stressed that the irregular variability of protean displays is not accidental but has been selected for in phylogeny. A number of poorly understood behavioural aspects of the ecology of predator-prey relationships are thus united in a single theory.