Population dynamics and the evolution of cooperation in group-structured populations
Microbes providing public goods are widespread in nature despite running the risk of being exploited by free-riders. However, the precise ecological factors supporting cooperation are still puzzling. Here, we consider the role of population growth and the repetitive fragmentation of populations into small colonies, as also studied in recent experiments. Individual-based modeling reveals that demographic fluctuations, which lead to a large variance in the composition of colonies, promote cooperation. Biased by population dynamics these fluctuations result in two qualitatively distinct regimes of stable cooperation. First, if the level of cooperation exceeds a threshold, cooperators will take over the whole population. Second, cooperators can also emerge from a single mutant leading to a stable coexistence between cooperators and free-riders. We find the frequency and size of population bottlenecks as well as growth dynamics to be the major ecological factors determining the regimes and thereby the evolutionary pathway towards cooperation.