Using community and population approaches to understand how contemporary and historical factors have shaped species distribution in river ecosystems

To examine how the employment of both community- and population-level approaches can provide a wider view of the importance of contemporary and historical factors on current species distribution. We posit that community ecology should provide more information about contemporary factors, whereas population genetics should provide better information about historical factors. Rivers of the western Mediterranean Basin, including four subregions differing in geological history: the Iberian Plate, Transitional, Betic and Rif. For a community-level approach, Trichoptera richness and community composition were compared between subregions using species accumulation curves and a correspondence analysis. For a population-level approach, the mtDNA cytochrome C oxidase subunit I (COI) gene of specimens of the Trichoptera midstream-lowland species Chimarra marginata (L.) was sequenced and analysed using phylogeographical methods. The community approach revealed that historical events had more influence on headwater communities than contemporary ecological factors, whereas historical events had negligible influence on midstream-lowland communities. In midstream-lowland sites, however, the population approach showed that the genetic structure of C. marginata differed significantly between subregions and revealed patterns of historical gene migration. In terms of species richness, the Rif subregion had the lowest value per basin due to local climatic features and isolation. Both community- and population-level approaches yielded information about the effects of historical factors on species distribution. However, the importance of historical events on current Trichoptera communities depends on the river zonation. Unlike headwater sites, midstream-lowland sites showed signs of historical events at the population level but not at the community level at the scale used, indicating that both approaches should be employed together in biogeographical studies. Lack of detection of historical events at the community level does not necessarily mean that they are negligible. Most likely, the organizational level used is not appropriate. We also stress the importance of implementing conservation measures for rivers in the western Mediterranean, especially under future scenarios of climate change and human disturbances in the Mediterranean Basin.