Habitat loss and fragmentation continue to account for most biodiversity loss worldwide. Understanding how local communities on fragments disassemble can help to understand the community-level mechanisms that drive this loss. Fragmentation can alter local community structure via both stochastic processes (e.g. extinction and colonization) and deterministic processes (e.g. environmental niche differentiation) resulting in local communities on fragments that are, respectively, either more different from one another (have higher site to site beta diversity), or more similar (have lower site to site beta diversity). We examined the effects of forest fragmentation in a controlled, replicated experiment at Wog Wog in southeastern Australia for a diverse beetle assemblage (325 species). We examined community responses for two years before through five years after experimental fragmentation.
While local richness did not decline, fragmentation reduced beta diversity so that sites within fragments became more similar to one another in their species composition than sites in control “fragments” were to one another. This effect was likely mediated through the exchange of individuals between fragments and the pine plantation matrix, where richness and beta diversity were lower than the original eucalypt habitat. This reduction in beta diversity suggests that habitat fragmentation promotes the deterministic, relative to the stochastic, components of community disassembly, illustrating how fragmentation alters communities not only through the extinction of populations but by affecting the broader mechanisms which structure communities.