Taxonomic turnover and northward phylogenetic clustering reveal evidence for environmental filtering in structuring Trichoptera communities across Europe

Abstract

Abstract A fundamental question in macroecology is how contemporary and historical environments, species interactions and evolutionary processes contribute to determining community structure and shape current large‐scale taxa distributions. We used a novel perspective simultaneously considering taxonomic, functional, and phylogenetic diversity to elucidate how these factors have shaped regional diversity patterns in composition of Trichoptera (Insecta) at the genus level among 62 mountain stream reaches located across six regions from Morocco to Sweden. The biogeographical range paradigm postulates declining diversity with latitude, but our results showed that taxonomic diversity was unrelated to latitude and local richness was similar in both previously glaciated and unglaciated southern regions. Also, taxonomic β‐diversity across regions was mostly driven by turnover rather than the expected nestedness component. High taxonomic diversity and several indicator genera (i.e. genera characteristic of any specific region) were found in Mediterranean regions, but also in the Carpathians and across central‐eastern Europe. Functional traits revealed phylogenetic trait conservatism. Phylogenetic diversity and functional richness did not decrease with latitude. Phylogenetic structure of central and eastern communities was clustered (i.e. communities composed by closely related genera), whereas south‐western communities were phylogenetically overdispersed (i.e. less closely related than expected by chance). Overall, latitudinal patterns of taxonomic turnover and variable phylogenetic community structure indicate an important role of contemporary ecological conditions in structuring community composition, probably by environmental filtering. However, the signature of biogeographical history is also relevant to understanding the large‐scale distribution of taxa. The permanence of caddisfly communities in temperate regions during Pleistocene glaciations demonstrates the presence of refugia there and, therefore, broadens the spatial extent of refugia beyond Mediterranean areas. This contrasts with theories which placed refugia exclusively in Mediterranean areas.