THE EFFECT OF A CHANGE IN FORAGING OPTIONS ON INTAKE RATE AND PREDATION RATE

We consider an animal making a single choice between options that diff er in terms of the resulting energetic gain and probability of predati on. We assume that the animal chooses the option that maximizes its fi tness and investigate how the animal's energetic gain and probability of being killed change when the environment is changed. It is shown th at two aspects of the change strongly influence the results. One aspec t is how the change differentially affects the foraging options. If an improvement in the food supply has more of an effect on good than on poor sources of food, intake rate will tend to increase. If the improv ement has more of an effect on poor options, then intake rate may decr ease. The other aspect is whether the change is transitory or relative ly permanent. In a particular model, short-term changes that improve t he environment increase intake rate, whereas long-term improvements re sult in intake rate's remaining constant or decreasing. We discuss our results in the context of other work on changes in foraging options a nd attempt to give general reasons for paradoxical effects.