As communities grow in size over time from just a few people to hundreds and then thousands, members frequently find that they feel less involved, that the community lacks relevance, and that their trust in the community as a friendly place is gone. A prime example of this is online message boards or other communities developed around social interaction which are renowned for becoming bogged down in endless arguments and spamming as they increase in size. The same ideas apply to online trading systems such as eBay which require a far higher degree of trust and reliability. We follow a game theoretic model of frequent interactions over time between reactive agents to examine the conditions under which a population is likely to find a set of strategies which allow them to cooperate a sufficient percentage of the time to remain viable.

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