Among-taxon congruence in biodiversity patterns: can stream insect diversity be predicted using single taxonomic groups?

The utility of single taxonomic groups as indicators of biodiversity variation in other taxa has recently gained increasing attention, but such studies on stream organisms are lacking. We studied the diversity patterns of mayflies, stoneflies, caddisflies, and chironomid midges across 110 headwater streams in Finland. Specifically, we examined if species richness and assemblage composition showed similar variation among the taxonomic groups across environmental gradients and if a single taxon could be used as a predictor of diversity in the other groups. Species richness and composition in different taxa exhibited slightly different relationships to environmental gradients, leading to low degrees of concordance. The diversity of mayflies and chironomids showed strongest relationships with stream acidity and water colour, whereas stoneflies and caddisflies exhibited more complex correlations with geographical location and local environmental variables. The overall assemblage composition, however, exhibited significant among-taxon congruence, as shown by Mantel tests. However, even these correlations remained rather low, thus limiting their potential for conservation purposes. Overall, our results do not support the use of single taxonomic groups as indicators of insect biodiversity in headwater stream ecosystems. Alternative approaches for lotic biodiversity assessment (e.g., morphospecies, higher-taxon richness, and environmental diversity) should thus be examined in future studies.