Limited Dispersal Drives Clustering and Reduces Coexistence by the Storage Effect.

Temporal variation can facilitate the coexistence of competitors through the temporal storage effect. However, this theoretical result was derived with the assumption that species have high dispersal rates. Here, I show that limited dispersal diminishes the storage effect in the classical lottery model. Populations become highly clustered during invasion, and population growth rates and extinction probabilities are functions of cluster size. I adopt the term "nucleation" from the physics literature to describe these characteristics. I developed approximations that incorporated nucleation to capture the spatiotemporal dynamics of the simulated model. Using analytical results from these approximations, I show that limited dispersal dampens asynchronous fluctuations in reproduction between species. This makes species appear to be more similar in their growth rate responses to the environment, thus reducing the potential for the storage effect. Theoretical results lead to simple rules relating average dispersal distances to relative reductions in potential coexistence. To demonstrate their use, I perform a preliminary analysis of two plant communities: tropical trees and desert annuals. In both communities, small-seeded species that disperse short distances on average have the strongest reductions in potential coexistence; species with wind- or animal-driven dispersal disperse farther distances, on average, and experience moderate or small reductions.