Learning to avoid aposematic prey

The evolution of prey warning coloration is, literally, a textbook example of Darwinian adaptive evolution by natural selection. The cornerstone of this evolutionary process is a predation event, the dynamics of which are poorly understood. Aposematic (warningly coloured) prey. are relatively unpalatable and their conspicuous appearance should enable predators to avoid them, but such is not always the case. Based on models of conditioned learning, it has been assumed that the number of aposematic prey that a predator will attack as it learns to avoid such prey should be constant or declining as the prey's abundance increases. However, empirical studies have shown that predators make more attacks on aposematic prey when those prey are more common. I suggest that this failure of theory to predict behaviour probably arises from limitations of the learning models in question. Rather than using mechanistic models of conditioned learning, I used signal detection theory to provide a functional characterization of the uncertainty that inexperienced predators encounter when learning to distinguish prey types. This characterization explains otherwise puzzling data on predation on aposematic prey and can offer insight on the selective pressures driving the evolution of aposematism and mimicry. (c) 2005 The Association for the Study of Animal Behaviour Published by Elsevier Ltd. All rights reserved.