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 differ in terms of the resulting energetic gain and probability of predation. We assume that the animal chooses the option that maximizes its fitness and investigate how the animal's energetic gain and probability of being killed change when the environment is changed. It is shown that two aspects of the change strongly influence the results. One aspect 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 improvement has more of an effect on poor options, then intake rate may decrease. The other aspect is whether the change is transitory or relatively permanent. In a particular model, short-term changes that improve the environment increase intake rate, whereas long-term improvements result in intake rate's remaining constant or decreasing. We discuss our results in the context of other work on changes in foraging options and attempt to give general reasons for paradoxical effects.