Stabilization of species coexistence in spatial models through the aggregation–segregation effect generated by local dispersal and nonspecific local interactions

Spatial interactions are widely acknowledged to play a significant role in sustaining diversity in ecological communities. However, theoretical work on this topic has focused on how spatial processes affect coexistence of species that differ in their strategies, with less attention to how spatial processes matter when competitors are equivalent. Furthermore, though it is recognized that models with local dispersal and local competition may sustain higher diversities of equivalent competitors than models in which these are not both localized, there is debate as to whether this reflects merely equalizing effects or whether there is also a stabilizing component. In this study, we explore how dispersal limitation and nonspecific local competition influence the outcome of species coexistence in communities driven by stochastic drift. We demonstrate that space alone acts as a stabilizing factor in a continuous space model with local dispersal and competition, as individuals of rare species on average experience lower total neighborhood densities, causing per capita reproductive rates to decrease systematically with increasing abundance. These effects prolong time to extinction in a closed system and enhance species diversity in an open system with constant immigration. Fundamentally, these stabilizing effects are obtained when dispersal limitation interacts with local competition to generate fluctuations in population growth rates. Thus this effect can be considered a fluctuating mechanism similar to spatial or temporal storage effects, but generated purely endogenously without requiring any exogenous environmental variability or species dissimilarities.