Benthic insects in Swedish lake-outlet streams: patterns in species richness and assemblage structure


Address for correspondence: Dr Björn Malmqvisl, Department of Animal Ecology, University of Urneå, S 901 87 Umeå, Sweden


1. We studied how species richness of three hierarchical insect species groups, namely all benthic, lotic and filtering taxa, were related to a number of environmental variables in a data set from fifteen Swedish lake outlets.

2. In partial least-squares analyses, we found that size-related factors (stream width, discharge) and velocity-related factors (current velocity, substratum particle size) were positively associated, and productivity-related factors (chlorophyll a, seston energy, conductivity) negatively associated, with the species richness of the three groups.

3. The weak and negative relationship of richness with productivity largely negated theoretical predictions, whereas the species-environment results corroborated earlier findings from running water systems.

4. The most important factors associated with the species composition of the lake outlets studied included pH, lake area, discharge, channel width and detritus.

5. Of the filter feeders, most species of blackflies (Diptera: Simuliidae) showed a negative relationship with pH.

6. A nested subset analysis demonstrated that species-poor sites did not have a subset of species found at more species-rich sites in any of the three hierarchical groups.