Abstract：
Understanding the conditions for maintaining cooperation in groups of unrelated individuals despite the presence of non-cooperative members is a major research topic in contemporary biological, sociological, and economic theory. The N-person snowdrift game models the type of social dilemma where cooperative actions are costly, but there is a reward for performing them. We study this game in a scenario where players move between play groups following the casual group dynamics, where groups grow by recruiting isolates and shrink by losing individuals who then become isolates. This describes the size distribution of spontaneous human groups and also the formation of sleeping groups in monkeys. We consider three scenarios according to the probability of isolates joining a group. We find that for appropriate choices of the cost-benefit ratio of cooperation and the aggregation-disaggregation ratio in the formation of casual groups, free-riders can be completely eliminated from the population. If individuals are more attracted to large groups, we find that cooperators persist in the population even when the mean group size diverges. We also point out the remarkable similarity between the replicator equation approach to public goods games and the trait group formulation of structured demes.
摘要：
尽管存在非合作成员，但了解在不相关的个人群体中保持合作的条件是当代生物学的一个主要研究课题，社会学,和经济理论。N人雪堆游戏模拟了合作行动代价高昂的社会困境类型，但是表演是有奖励的。我们在玩家遵循休闲小组动态在游戏小组之间移动的情况下研究此游戏，群体通过招募分离株而成长，并通过失去随后成为分离株的个体而缩小。这描述了自发人类群体的大小分布以及猴子中睡眠群体的形成。我们根据分离株加入群体的概率考虑三种情况。我们发现，在形成临时团体时，对于适当选择合作的成本效益比和聚集分解比，可以从人口中完全消除搭便车者。如果个人对大型团体更有吸引力，我们发现，即使平均群体规模不同，合作者也会在群体中持续存在。我们还指出了公共物品游戏的复制方程方法与结构化恶魔的特质组表述之间的显着相似性。
