Prey Selection By Predators Depleting a Patch; an Ess Model

Abstract

An important group of prey selection models are static optimal diet models in which it is assumed that a predator maximizes its instanteneous rate of gain (energy per unit of time). In these models the encounter rate with different prey types is constant. However, when predators forage in patches, depletion will occur and therefore this assumption is relaxed in this paper. As a consequence, the resource value of the habitat and the number of predators in the patch influence prey choice decisions. For this reason a game theoretical approach is used. When the quality of the habitat is high, the less profitable prey should never be accepted, independent of the number of predators in the patch. When the quality of the habitat is low, a predator searching a patch alone should always accept the less profitable prey. When searching a patch together with others, the most profitable prey are also depleted by these competitors. Thus, competition for these prey occur and the ESS is to reject the less profitable prey at first but accept them after a switch point. This ESS causes partial preference; a prey type is not always accepted or always rejected. The ESS switch point depends on the number of predators in the patch. When a large number of predators deplete a patch, the best strategy is to maximize the instantaneous rate of gain. When there are few predators, switching should occur earlier in time than predicted from instanteneous rate maximalization. It is concluded that not only the value of the less profitable prey is important in prey selection but also the number of predators in the patch and the value of the habitat. Thus, prey selection and patch time allocation are interdependent decisions for predators foraging in a patchy environment.