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 acti vity was studied using yellow water traps, whereas suitable larval hab itats were determined using emergence traps. While 24 species emerged from the soils, 45 flew above the four sites. The number of species em erging from each site was nearly identical. However, the highest numbe r of individuals emerged from the heathland and numbers rapidly declin ed towards the pond banks. On the contrary, the greatest aerial activi ty occurred in the woodlot and near the pond banks. Fourteen times les s flying activity was found above the dry heathland. The latter appear ed 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 ad ults differed among the dominant species. The species assemblage could not be fully explained within the spatial limits of the four sites. C onsidering the species' behaviour, it is suggested that immigration of species and individuals from other sites should explain these differe nces. The study, which is supported by four other research works, emph asizes the role of key resource played by ecotonal zones between aquat ic and terrestrial ecosystems in the persistence of species over a lar ger set of habitats. Considering the complementarity of habitats is es sential to explain diversity patterns in species which need different space units to complete their life-cycle.