Asynchronous snowdrift game with synergistic effect as a model of cooperation

The snowdrift (or chicken) game emerges as a new paradigm in the study of nonkin cooperation in animals. Many situations, for example, cooperative hunting, group foraging, territorial defense, predator watching, or parental care, can be adequately described as a snowdrift game. In this paper, we investigate the asynchronous version of the game in which, contrary to the rather unrealistic assumption of simultaneous moves, one of the players acts first and the other responds by knowing its decision. Players are assigned to be first or second movers randomly and with the same probability. We found that both a synergistic effect of cooperation (i.e., cooperative effort is better than the sum of the individual efforts) and population structure (low dispersal, spatial confinement, or group formation) are crucial for mutual cooperation to emerge. Otherwise, only one of the players will carry the burden of cooperation. Copyright 2006.chicken game; cooperation; game theory; snowdrift game