Negative and matrix-dependent effects of dispersal corridors in an experimental metacommunity.

Negative effects of habitat fragmentation are well-known phenomena in ecology, and the use of corridors is one suggested remedy to ameliorate community disassembly. Most experiments of landscape structure, however, do not consider matrix quality and environmental conditions, despite their potential to affect both landscape permeability and population densities. For the first time in fragmented landscapes, we simultaneously investigated the effects of local disturbance, dispersal corridors, matrix quality, and environmental stress, as well as their interactions, on species richness and abundance. We used a natural micro-ecosystem of bryophyte patches with microarthropods as a model system. Contrary to expectations, there were no negative responses to fragmentation of large continuous habitats. Surprisingly, connecting fragmented patches with dispersal corridors had negative effects on the abundance and species richness of the most species-rich group, oribatid mites. It had also negative effects on the abundance of collembolans and predatory mites in landscapes with complex matrix, which was also generally detrimental. Environmental stress was detrimental for all taxa but interacted with matrix type for oribatid species richness and juvenile oribatid abundance. Our results indicate that interactions can strongly alter community responses to common explanatory factors such as fragmentation, disturbance, connectivity, and environmental quality. Future studies of metacommunity dynamics need to consider the potential for such interactions in order to produce robust predictions of spatially structured landscapes.