Coexistence and cooperation in structured habitats

Many natural habitats are structured, which imposes certain environmental conditions on extant populations. Which conditions are important for coexistence of diverse communities, and how social traits in such populations stabilize, have been important ecological and evolutionary questions. We investigate a minimal ecological model of microbial population dynamics, that exhibits crucial features to show coexistence: Populations are repeatedly separated into compartmentalized habitats on a timescale typically longer than growth. In this framework, we consider several scenarios for possible interactions between different strains and their environments, which includes sharing a common nutrient source or expression of public goods that potentially increase population size. Examples for these public good dynamics are collective resistance against antibiotics, and enhanced iron-availability due to pyoverdine. We show that the two features of a long mixing timescale and spatial compartmentalization are already enough to enable coexisting strains. In the case of public goods, stable coexistence immediately entails cooperation.