Cooperative and Noncooperative Behavior in Animals

Put in one sentence, the central message of this article is: There are theoretical reasons and empirical evidence to suggest that the performance of cooperative and noncooperative behavior by animals in many situations is best explained by considering both fitness benefits and the contributions of other group members to cooperative behavior. The formal model presented here indicates one way in which fitness benefits and the actions of other group members can be combined to yield predictions about the performance of cooperative and noncooperative behavior. This model is contrasted with the population genetics models applying to cooperative and noncooperative behavior. These latter models predict only the presence or absence of cooperative and noncooperative behavior from fitness considerations; they do not predict the actual, quantifiable amount of each kind of behavior, and they do not recognize the possibility that the amount of a behavior may be adjusted in a manner contingent upon the behavior of other animals in a group. It is suggested that the model presented here be used as a heuristic device to stimulate and guide detailed, quantitative studies of the dynamics of cooperative and noncooperative behavior in animal groups. Three general hypotheses that are generated by the model and that can be used to guide research and aid in interpretation are discussed. The three hypotheses concern how investment in cooperative and noncooperative behavior changes with group size, the presence of equilibrium patterns in certain situations involving cooperative behavior, and the adjustment to changes in the unit costs of cooperative and noncooperative behavior. Several studies by which the hypotheses might be tested are briefly outlined, and finally two simplifying assumptions made in the construction of the model are discussed.