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.

Conceived to combat widescale biodiversity erosion in farmland, agri-environment schemes have largely failed to deliver their promises despite massive financial support. While several common species have shown to react positively to existing measures, rare species have continued to decline in most European countries. Of particular concern is the status of insectivorous farmland birds that forage on the ground. We modelled the foraging habitat preferences of four declining insectivorous bird species (hoopoe, wryneck, woodlark, common redstart) inhabiting fruit tree plantations, orchards and vineyards. All species preferred foraging in habitat mosaics consisting of patches of grass and bare ground, with an optimal, species-specific bare ground coverage of 30–70% at the foraging patch scale. In the study areas, birds thrived in intensively cultivated farmland where such ground vegetation mosaics existed. Not promoted by conventional agri-environment schemes until now, patches of bare ground should be implemented throughout grassland in order to prevent further decline of insectivorous farmland birds.

As many other birds breeding in agricultural areas, the common redstart declined strongly in many Central European countries over the last 60 years. The destruction of traditionally managed orchards, an important breeding habitat in Central Europe, is a relevant cause. An additional factor for the decline of this species could be the intensified management of the ground vegetation in orchards through reducing food availability and lowering prey detectability and accessibility. In this study we examined the importance of surfaces with sparse vegetation for the location of redstart territories and for foraging. To validate the results of these field studies we made habitat-choice experiments in aviaries with captive birds. Territories occupied by redstarts in orchards of northwestern Switzerland contained a significantly higher proportion of surfaces with sparse vegetation than unoccupied control sites. Redstarts made almost five times more hunting flights into experimentally established ruderal vegetation strips than into adjacent unmown meadows. No difference was observed when the meadow was freshly mown. Vegetation height and the proportion of open ground surface correctly predicted the vegetation type for hunting in 77% of the cases. Experiments in aviaries offering two types of sparse vegetation and a dense meadow supported the results of the field experiments. Even a four-fold increase of the food abundance in the meadow did not lead to a noticeable change in preference for the sparse vegetation types. For the conservation of the common redstart, not only traditionally managed orchards with tall trees with cavities should be preserved but also areas with sparse vegetation should be favored.

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