Relationships between structure and function in streams contrasting in temperature

P>1. We studied 10 first-order Icelandic streams differing in geothermal influence in separate catchments. Summer temperature (August-September) ranged between 6 and 23 degrees C. 2. Macroinvertebrate evenness and species overlap decreased significantly with temperature whereas taxon richness showed no response. In total, 35 macroinvertebrate species were found with Chironomidae the dominant taxonomic group. Macroinvertebrate density increased significantly with temperature. Dominant species in the warm streams were Lymnaea peregra and Simulium vittatum. Algal biomass, macrophyte cover and richness were unrelated to temperature. Densities of trout (Salmo trutta), the only fish species present, reflected habitat conditions and to a lesser degree temperature. 3. Density of filter-feeders increased significantly with temperature whereas scraper density, the other dominant functional feeding group, was unrelated to temperature. Stable isotope analysis revealed a positive relationship between delta