Drying has limited effects on macroinvertebrate assemblages of alpine river networks

Alpine fluvial networks experience rapid climate change with extensive consequences on hydrology, including an increase in the prevalence and severity of flow intermittence and its constraint on aquatic assemblages. While the ecological effects of intermittency are relatively well documented in some biogeographic regions (e.g., Mediterranean), they are essentially unknown for alpine streams. We characterized flow intermittence and associated local and regional responses of macroinvertebrate assemblages across 75 headwater streams in 4 glacierized Alpine catchments over one year. Flow intermittence had a temporal effect on assemblages through localized drying, rather than a spatial effect related to stream network fragmentation. Specifically, high drying frequency reduced α and β diversity through homogeneous selection of resilient taxa and shifted community composition towards higher resilience. However, the structuring effects of flow intermittence on taxonomic and functional β diversity were mild. Local environmental conditions consistently had a stronger influence on assemblage composition than flow intermittence. Benthic macroinvertebrates in alpine stream networks of glacierized catchments are relatively well adapted to moderate flow intermittence, resulting from the environmental filtering of relatively harsh environmental conditions of alpine landscapes. As flow intermittence becomes more intense and prevalent with environmental change in alpine landscapes, biological resilience thresholds could be exceeded with more severe consequences on stream biota.