Metacommunity structure: Synergy of biotic interactions as selective agents and dispersal as fuel

The relative importance of regional and local processes in determining community structure is a long-standing problem in community ecology. This is especially problematic in communities from highly connected habitats, which undergo two opposing forces: differences in environmental conditions of the habitats lead to divergence of the communities, while the dispersal of individuals leads to convergence of the communities. Using a transplant experiment, we experimentally showed that biotic interactions, have a predictable, deterministic impact on zooplankton community structure in a metacommunity of highly interconnected shallow ponds. Fish predation and presence of abundant macrophyte cover. rapidly structured regional communities of zooplankton, both in terms of relative abundances and of cladoceran species richness. Moreover, we could use the relations between the experimentally manipulated environmental conditions and the observed experimental communities to successfully classify the contrasting local communities found in the original neighboring ponds, thus directly relating the experimental results to the actual field situation. Notwithstanding the observed strong impact of local biotic conditions, we also showed that dispersal had an influence on community structure and species richness. Dispersal increased species richness of cladocerans by three species and influenced zooplankton community structure. More-over, dispersal actually made the response to local conditions more deterministic.