Supplementary material from "The effects of anisotropic dispersal on species coexistence in a metacommunity"

Dispersal is a ubiquitous process occurring in any ecosystem, with a critical role in the regional coexistence of species that cannot coexist locally. However, previous studies have typically focused on a specific scenario where dispersal is isotropic, which leaves the consequence of anisotropic, directionally skewed dispersal largely unexplored despite its prevalence in natural ecosystems. In this study, we used simulations to study whether the anisotropy of dispersal promotes or hinders species coexistence in a metacommunity. We found that dispersal anisotropy plays a decisive role in species coexistence—with coexistence promoted when dispersal is more directed orthogonally to an environmental gradient, while it being less likely when dispersal is primarily parallel with the gradient. This occurred because dispersal directed orthogonally to the background environmental gradient transports individuals produced in “good” habitats to other good habitats, creating conditions that favour several spatial coexistence mechanisms, such as spatial storage effects and fitness-density covariance. We conclude that the effect of anisotropic dispersal could be diverse and therefore it is necessary to consider the anisotropy and the distribution of environments for a better understanding of species coexistence in a metacommunity.