Stochastic Spatial Models of Host-Pathogen and Host-Mutualist Interactions II

Plant community structure is shaped by interactions among plants and their pathogens and mutualists (collectively called symbionts). Some symbionts are highly specialized, others are generalists, adding to the complexity of interactions. The development of a conceptual framework that is based on idealized models is a necessary step in reaching a level of understanding that would allow us to predict outcomes of these interactions. In this paper, we introduce spatially explicit, stochastic models of multispecies host-symbionts interactions with a specific focus on how the degree of specialization affects coexistence of multiple hosts and their symbionts, and, in case of coexistence, what spatial patterns result. Our rigorous results, supplemented by simulations, give a complete description of the behavior of these host-symbionts models. It is proved analytically that generalist symbionts have only a limited effect on the structure of host communities which, in contrast, can be significantly altered by specialist mutualists, with the most beneficial mutualist together with its most preferred hosts outcompeting all the other species. Numerical simulations further suggest that, in the neutral case, specialist pathogens promote the local diversity whereas specialist mutualists lead to a coarse-grained habitat. This paper also contains conjectures for future research directions.