Local biodiversity and multi-habitat use in empidoid flies (insecta: Diptera, empidoidea)

The empidid fauna of four small adjacent biotopes bordering a pond was investigated for 2 consecutive years in Brittany (France). Adult activity was studied using yellow water traps, whereas suitable larval habitats were determined using emergence traps. While 24 species emerged from the soils, 45 flew above the four sites. The number of species emerging from each site was nearly identical. However, the highest number of individuals emerged from the heathland and numbers rapidly declined towards the pond banks. On the contrary, the greatest aerial activity occurred in the woodlot and near the pond banks. Fourteen times less flying activity was found above the dry heathland. The latter appeared to be a site of larval growth but mating and feeding of the adults took place in the woodlot. Reproduction sites and space used by the adults differed among the dominant species. The species assemblage could not be fully explained within the spatial limits of the four sites. Considering the species' behaviour, it is suggested that immigration of species and individuals from other sites should explain these differences. The study, which is supported by four other research works, emphasizes the role of key resource played by ecotonal zones between aquatic and terrestrial ecosystems in the persistence of species over a larger set of habitats. Considering the complementarity of habitats is essential to explain diversity patterns in species which need different space units to complete their life-cycle.