Effects of land cover type on community structure and functional traits of alpine stream benthic macroinvertebrates

1. In the European Alps, due to the current changes in land use driven by different social and economic factors, grasslands and pastures are being increasingly replaced by forests. Whereas many studies have focused on the impacts of urbanisation and intensive agricultural activities, no study has evaluated the effects of changes among types of natural to semi-natural land cover in the Alps with a focus on lotic environments.
2. Here, combining taxonomic and functional approaches, we show the effects of four different alpine land cover types (rocks, grasslands, coniferous forests, valley bottom pastures) on stream benthic macroinvertebrate communities. Irrespective of elevation, grasslands and pastures exhibited unpredicted similarity in terms of the composition of the macroinvertebrate assemblages and hosted the highest diversity of benthic organisms, whereas in each of the other land cover types, the density and diversity of the faunal assemblages showed distinct and characteristic values.
3. When analysing the functional diversity decomposed to richness, evenness, and divergence components, grasslands and pastures again showed a similar trend, being characterised by high levels of resource exploitation and niche differentiation, with the potential to host additional organisms. However, as expected, differences driven by land cover type and elevation emerged when examining the single functional traits, since elevation played a major role in terms of the distribution of traits conferring resistance and resilience.
4. Our results demonstrate that land cover type is a prominent factor influencing the taxonomic and functional variety of stream benthic macroinvertebrate communities. Moreover, alpine grasslands contained an unexpected diversity of aquatic insects, as previously assessed for other organisms (e.g. plants and snails). Overall, our study highlights the importance of the preservation of the diversity of habitats in the alpine region, with a special focus needed for valuable semi-natural landscapes, such as grasslands and pastures, particularly in a time of increasing intensification and abandonment of lands in the alpine context.