Experimental droughts in mesocosms reveal a gradient of tolerance in Alpine stream macroinvertebrates

Abstract Prolonged droughts, driven by climate change and human pressures on water resources, are increasing in frequency and intensity, particularly impacting Alpine rivers. Benthic macroinvertebrates are one of the most important structural and functional components of Alpine lotic ecosystems. We hypothesize that a prolonged drought will cause an alteration in the taxonomic richness, functional composition, and abundance of the macrobenthic community over time, with an impact that could, however, be different for the different groups considered. Here, we conducted a mesocosm experiment to assess the resilience of various macroinvertebrate taxa exposed to simulated drought conditions. We have observed a general trend of rapid decline in both macroinvertebrate abundance and diversity, which, however, shows interesting differences between the different groups. For instance, some taxa such as Rhithrogena , Ecdyonurus , and Crenobia alpina exhibited a more rapid negative response, whereas others, such as Lumbricidae, Chironomidae, and Athericidae demonstrated greater resistance, aggregating and surviving for longer periods in the moist substrate. Data analysis performed with Outlying Mean Index revealed five tolerance‐based groups, ranging from highly drought‐sensitive to more resistant taxa. This study contributes to our understanding of drought resistance mechanisms in macroinvertebrate communities and highlights the ecological consequences of prolonged drying on biodiversity. The findings underscore the necessity for water management strategies that consider the preservation of natural refugia and the maintenance of permanent flow regimes to support drought‐sensitive communities, particularly in vulnerable Alpine ecosystems.