Models and Mechanisms of Frequency-Dependent Predation

Positive frequency-dependent predation, or switching, occurs when the relative risk of a particular prey type increases with its relative density. Each of the four primary mechanisms of switching identified by Murdoch et al. (1975) can be related to the components of prey risk, including the efficiency of the search path and the probability of detection. Models of frequency-dependent predation can be categorized as either mechanistic or descriptive. Two descriptive models have been proposed by Elton and Greenwood (1970) and by Manly (1973). In order to develop a more general model, I combined features of both earlier models. I then evaluated these three models in terms of their ability to fit both theoretical and empirical examples of switching. All the models fit the empirical data reasonably well, but the new model fits the theoretical case better than the other descriptive models do. One advantage of the new model is the greater insight it provides into the behavioral mechanisms underlying frequency-dependent predation.