INTERGROUP COMPETITION AND STABLE GROUP SIZES

The stability of the sizes of foraging groups of animals is reviewed w ith a special emphasis on the effect of inter-group competition. A sim ple model, in which cooperation, within-group and inter-group competit ion are explicitly accounted for, shows that when resources are scarce and patchy, inter-group competition tends to keep animals within thei r groups, even when these groups are overpopulated. The model's conclu sions are in accord with empirical observations indicating that animal s tend to forage in groups that are larger than the expected optimal s ize. (C) 1995 The Association for the Study of Animal Behaviour