SOCIAL FORAGING - PRODUCING AND SCROUNGING IN A STOCHASTIC ENVIRONMENT

The producer-scrounger paradigm applies to an array of interactions influencing the economics of sociality; we apply the concept to group foraging. Producers generate opportunities to exploit resources; scroungers attempt to sequester some of the resources producers discover. We develop two models of producing and scrounging in foraging groups of fixed, finite size. In the producer-priority model scrounging reduces a producer's expected food intake, but the reduction does not depend on the exact number of scroungers in the group. In the scramble-competition model a producer's expected food intake always decreases as the number of scroungers increases. Treating each model as an N-person game, we find stable numbers of producers and scroungers for different group sizes, food densities, physiologically required food-intake levels, costs of scrounging, and competitive abilities of producers. Solutions to our models assume that strategic efficiency reduces the individual's probability of starving. Stochastic variation in our models arises because the amount of food discovered varies randomly, and because the allocation of food items among foragers within a clump may also vary randomly. Previous producers-scrounger models are deterministic, so our stochastic models make a series of new predictions. We also discuss the importance of phenotypic plasticity in modeling complex organisms' social behavior, and examine possible co-operative restraints on scrounging. © 1991 Academic Press Limited.