The role of dispersal mode and habitat specialisation in metacommunity structuring of aquatic macroinvertebrates in isolated spring fens

The relevance of environmental and spatial processes for species distributions varies among environments and types of metacommunities. Here, for the first time, we use modern statistical approaches to test the contribution of these two processes in structuring ecologically unique and threatened biotas of insular spring fens. We applied two species categorisations, common/rare and generalists/specialists, to disentangle the roles of dispersal capacity and habitat specialisation. In accordance with current understanding of headwater ecosystems, we found that environmental processes played a major role in most of the spring fen taxonomic and functional groups. However, we observed significant spatial structure in passive dispersers (Clitellata, a class of annelid worms), common species and habitat specialists. Spatial processes played the leading role in structuring the metacommunity of passively dispersing specialists. In contrast, all analysed insect groups, even those known to be poor dispersers, were able to reach virtually all favourable sites. We conclude that dispersal mode (active versus passive) and, to a lesser extent, habitat specialisation are the main factors determining the mechanism of spring fen metacommunity structuring.