A social dilemma structure in diffusible public goods

Encouraged by the interaction between two species of microbes, in which one species is capable of replenishing the public resources and the other is not, the dilemma structure (the long-term sustainability of the population) hidden in a system where public goods are defined as diffusible was examined. In a series of simulations in which the three major parameters governing the dynamics of the system were varied, following the effect of the spatial structure that results from resource diffusion and distribution, the dynamics show a rich diversity, including cooperator-dominated, extinct, and coexistent results. If the dilemma is strong, the chance of surviving cooperators is small and the population tends to extinction even though coexistence is possible. By contrast, if a weak dilemma is given, the affluent resources make cooperators dominant over defectors.