PRODUCERS, SCROUNGERS, AND GROUP FORAGING

We have developed a model that reconciles information-sharing and producer-scrounger models of group foraging. Our model includes producers, scroungers, and an opportunistic forager that can both produce and scrounge but with reduced efficiency. We show that these three strategies can coexist only in the unlikely case that the opportunist's loss in searching ability is exactly equal to its gain in scrounging ability. However, all pairs of strategies can coexist. Three parameters control the proportions of coexisting strategists: the degree of compatibility between the opportunist's producing and scrounging activities; the proportion of food patches that are shared with scrounging individuals; and the effective group size. When there is little incompatibility between producing and scrounging, opportunists will always be present, unless the producer is able to consume most of the patch without sharing. The opportunist strategy is always excluded when there is a high degree of incompatibility between producing and scrounging. We consider the organismal and ecological factors that are likely to affect all three parameters. Our model predicts that scrounging behavior is likely to be selected in a wide range of foraging groups and that it may impose a considerable cost on sociality.