A comparison of foraging strategics in a patchy environment

In this paper we compare foraging strategies that might be used by predator s seeking prey in a patchy environment. The strategies differ in the extent to which predators aggregate in response to prey density. The approach to the comparison is suggested by the idea of,evolutionarily stable strategies . A strategy is said to be evolutionarily stable if it cannot be invaded by another strategy. Thus we examine scenarios where a small number of indivi duals using one strategy are introduced into a situation where a large numb er of individuals using the other strategy are already present. However, ou r foraging models do not explicitly incorporate predator population dynamic s, so we use net energy uptake as a surrogate for reproductive fitness. In cases where all of the patches visited by predators sustain prey population s, we find that for any pair of strategies one of them will have a higher n et energy uptake than the other whether it is the resident or the introduce d strain. However, which one is higher will typically depend on the total p redator population, which is determined by the resident strain. If the pred ators leave prey densities high, the more aggregative strain will have the advantage. If the predators reduce prey densities to low levels the less ag gregative strain will have the advantage. In cases where one strain of pred ators aggregates in response to prey density and the other does not, then t here might be patches which do not contain prey but do contain (nonaggregat ing) predators. In those cases, there is the possibility that whichever str ategy is used by the introduced strain will yield a higher energy uptake th an that used by the resident strain. This suggests that if some patches are empty of prey then aggregative and non-aggregative strategies may be able to coexist. (C) 1999 Elsevier Science Inc. All rights reserved.