The Evolution of a Special Class of Modifiable Behaviors in Relation to Environmental Pattern

Abstract

A simple model was used to compute the selective advantage of one kind of avoidance conditioning. The model was developed in terms of a predator exploiting a stochastic environment of models and indistinguishable Batesian mimics. Nonmodifiable predators that either always eat or always ignore are compared with modifiable predators that ignore for some time, N, once a debilitating model is eaten. Modifiable behavior was superior to nonmodifiable behavior only when models and mimics were clumped. This condition corresponded to one class of relatively predictable environments. Optimal waiting time, optimal N, was an increasing function of the mean clump size of models and the relative badness of models. Thus the model predicts that selection will adjust the waiting time of modifiable predators such that the predator will tend to skip over clumps of debilitating models and exploit the intervening clumps of mimics. Predators should skip further, wait longer, as models become more debilitating. Very long waiting times, N > 100 models and mimics, will sometimes be optimal if the clump size of models is very large. The implications of the model for the evolution of delayed learning, irreversible switches (N near infinity), and predators that modify N with experience are discussed. The model is briefly applied to the evolution of predator avoidance by tube-dwelling worms and to the foraging behavior of predators searching for hidden prey in order to indicate the range of possible applications.