Utrecht University School of Economics, Utrecht University, Kriekenpitplein 21-22, 3584EC Utrecht, The Netherlands.
J Theor Biol. 2019 Jan 7;460:18-36. doi: 10.1016/j.jtbi.2018.10.006. Epub 2018 Oct 6.
The common-enemy hypothesis of by-product mutualism proposes that organisms are more likely to cooperate when facing the common enemy of a harsher environment. Micro-foundations of this hypothesis have so far focused on the case where cooperation consists of the production of a pure public good. In this case, the effect of a harsher environment is ambiguous: not only a common-enemy effect is possible, but also an opposite, competing effect where the harsher environment reduces the probability of cooperation. This paper shows that unambiguous effects of a harsher environment are predicted when considering the realistic case where the collective good produced is excludable (in the sense that whether or not a player benefits from the collective good depends on whether or not he is contributing) and/or congestible (in the sense that the benefits the individual player obtains from the collective good are affected by the number of contributing players). In particular, the competing effect is systematically predicted for club goods, where defectors are excluded from the benefits of the collective good. A common-enemy effect is instead systematically predicted for charity goods, where cooperators are excluded from the benefits of the collective good. These effects are maintained for congestible club goods and for congestible charity goods. As the degree to which a collective good is excludable can be meaningfully compared across different instances of cooperation, these contrasting predictions for public good, charity goods and club goods yield testable hypotheses for the common-enemy hypothesis of by-product mutualism.
副产品互惠的共同天敌假说提出，当生物体面临更恶劣环境这一共同天敌时，它们更有可能进行合作。该假说的微观基础迄今为止一直集中在合作包括生产纯公共产品的情况下。在这种情况下，恶劣环境的影响是模棱两可的：不仅可能存在共同天敌效应，而且还可能存在相反的竞争效应，即恶劣环境降低了合作的可能性。本文表明，当考虑到所生产的集体产品具有可排他性（即玩家是否从集体产品中受益取决于他是否有贡献）和/或拥挤性（即个人玩家从集体产品中获得的收益受贡献者人数的影响）的现实情况时，可预测出明确的环境恶化的影响。特别是，对于俱乐部物品（即从集体物品中受益取决于玩家是否有贡献），系统地预测了竞争效应。相反，对于慈善物品（即合作方被排除在集体利益之外），系统地预测了共同天敌效应。这些效应对于拥挤的俱乐部物品和拥挤的慈善物品仍然存在。由于集体产品的可排他性程度可以在不同的合作实例中进行有意义的比较，因此对于公共产品、慈善产品和俱乐部产品的这些对比预测为副产品互惠的共同天敌假说提供了可测试的假设。
