Drivers and metacommunity perspective of differences in regional species richness between main chironomid taxa inhabiting temperate zone rivers.

Deterministic and stochastic drivers in metacommunities of main chironomid taxa were identified by an analysis of the taxa's local species richness (LSR), environmental and seasonal factors, and habitat species richness (HSR), in samples collected at the mid-European regional scale. Orthocladiinae LSR depended on Orthocladiinae HSR, while Chironomini LSR did not depend on Chironomini HSR. Environmental drivers and autumn (optionally with HSR) explained over 70% of Orthocladiinae LSR variance, while environmental factors (optionally with HSR) explained less than 40% of Chironomini LSR variance. In both taxa, stochastic processes dominated over deterministic ones because species random co-occurrence was more frequent than non-random co-occurrence. In each taxon, about 20% of species pairs were non-random. Yet, in the Orthocladiinae, no pairs, while in the Chironomini one third of pairs, were negatively associated. Only the Chironomini metacommunity was competitively structured. In the Orthocladiinae, deterministic drivers were more abiotic (higher number and greater impact of environmental factors, a seasonal factor, no negative species co-occurrences), while in the Chironomini, deterministic drivers were more biotic (negative species co-occurrences, competitive metacommunity structure, no seasonal factor, lower number and smaller impact of abiotic factors).