MACROINVERTEBRATE COMMUNITIES IN GLACIER-FED STREAMS: DISPERSAL CONSTRAINTS OF HABITAT LIMITATIONS?

A.M. Milner^1,2, J.E. Brittain³, E. Castella⁴, and G.E. Petts¹. ¹School of Geography and Environmental Science, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK, ²Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99775, ³Freshwater Ecology and Inland Fisheries Laboratory, University of Oslo, N-0318 Oslo, Norway, ⁴Laboratoire d'Ecologie et de Biologie Aquatique, University of Geneva, Geneva, Switzerland

Generalized additive models predicted macroinvertebrate taxonomic richness and individual taxon diversity at the reach level across seven European glacier-fed sites from a set of 11 environmental variables. Maximum water temperature and channel stability explained the most deviance in these models. Although dispersal abilities potentially allow a large pool of colonizers to become established in these types of streams, habitat conditions, particularly close to the glacier, restrict the community to a few specialized taxa. Where maximum water temperature is below 2 ^oC, Diamesinae chironomids are typically the sole inhabitants, but where T_max > 2 ^oC but < 4 ^oC, Orthocladiinae are found, and where channels are more stable, Tipulidae and Oligochaeta also occur. Above 4 ^oC, Perlodidae, Taenopterygidae, Baetidae, Simuliidae, and Empididae can be expected to be part of the glacier-fed river community, particularly in Europe. These taxa are similar across a wide latitudinal range in the Northern Hemisphere and the habitat limitations convey deterministic trends to the summer community in these streams. However, many glacier-fed streams are located on islands or in alpine areas and dispersal constraints play a major role in determining the macroinvertebrate community, even as habitat conditions ameliorate downstream of the glacier margin.