River network properties shape α-diversity and community similarity patterns of aquatic insect communities across major drainage basins

Abstract

Aim: Spatial dynamics and habitat connectivity affect community composition and diversity in many ecosystems. For many decades, diversity patterns in riverine ecosystems were thought to be related to local environmental conditions. Recent theoretical work, however, suggests that diversity in rivers is strongly affected by dispersal along the dendritic landscape structure and that environmental conditions are intrinsically linked to the network position. In this study we tested hypotheses on network position by relating river network geometry and connectivity to multi-level biodiversity patterns across large scales. Location: Three major alpine drainage basins in Switzerland were studied (Rhine, Rhone, Ticino), extending over an elevational gradient of > 2500 m and covering a total area of 41,285 km2. Methods: We sampled all may-, stone- and caddisfly species at 217 sites which representatively cover the three river networks. Using generalized additive models, we related diversity patterns in aquatic insects to centrality within the network as a direct river network property, and to catchment area and elevation, which are related to network position. Results: Centrality within the river network, and catchment area and elevation had significant and interacting effects on α-diversity and community similarity. Alpha diversity was lowest in peripheral headwaters and at high elevations. Species richness generally increased with increasing catchment area. Well-connected, central communities within the river network had greater α-diversity than more peripheral communities did. Elevation was a strong predictor of α-diversity, with the most diverse communities found at mid-elevation sites. Community similarity decreased with increasing along-stream distance between sites. Main conclusions: Our results highlight the fact that diversity patterns of aquatic insects in river systems are related to local factors such as elevation, but interact with network properties and connectivity along waterways, and differ among insect orders. These findings are consistent with dispersal-limited processes and indicate that riverine diversity should be addressed and protected taking the river network structure into account. © 2013 John Wiley & Sons Ltd.