Trends in species diversity of lotic stoneflies ( Plecoptera) in the Czech Republic over five decades

An unusual data set of Plecoptera, very sensitive aquatic insects, allow diversity changes to be estimated for 175 streams in the Czech Republic between two periods, 1955-1960 and 2006-2011. Substantial overall declines in Plecoptera biodiversity were found. Three-quarters of the species studied declined in their frequency of occurrence, 48% of which were estimated have undergone a reduction of >30%. Overall, streams either at lowland or submontane altitude, particularly large rivers, lost the most species. A significant decrease in local species biodiversity was found in streams up to 700m a.s.l., especially in small rivers. The taxonomic dissimilarity between contemporary and previous assemblages increased from montane to lowland altitudes (from 30 to 70%) and was the same in streams of different size (50%). Partitioning of dissimilarity showed that the overall change in dissimilarity was primarily driven by changes in species richness; however, species replacement was not negligible. The results demonstrated that aquatic insect biodiversity (Plecoptera in particular) is substantially declining in Europe, probably to a similar or greater extent than terrestrial insects, with potential implications for biodiversity of running waters. Plecoptera showed a complex response to habitat change, including loss of pollution-sensitive species and habitat-specialists as well as common species, which, in some cases, counterbalanced their losses by concurrent colonisation of new sites.