Dispersal kernels regulate environmental, biotic, and stochastic effects on the maintenance of metacommunity...

Dispersal regulates patterns of diversity in metacommunities, but a primary focus on dispersal rates may mischaracterize effects that actually arise from dispersal kernels. Kernels describe probabilistic movements between donor and recipient patches, with steep kernels displaying a rapid decline in dispersal probability with distance, and shallow kernels decaying gradually over longer distances. We used simulations to measure how kernels affect diversity across metacommunity scales and ecological contexts, and developed a novel approach quantifying the effects of environmental filtering, competition, stochasticity, and dispersal on fitness. Metacommunities with shallow kernels followed expectations: emigration increased α-diversity but decreased β-diversity and γ-diversity. Metacommunities with steeper kernels did not follow expectations: steep kernels maintained regional diversity by reducing interspecific competition and stochastic extinctions, while weakening the fitness benefits of low dispersal and costs of high dispersal. Our work suggests dispersal kernels and rates jointly regulate exposure to environmental variation and the balance of assembly mechanisms in metacommunities.