Environmental traits affect chironomid communities in glacial areas of the Southern Alps: evidence from a long-lasting case study

1. A collection of approximately 100 000 chironomids (Diptera; Chironomidae) inhabiting glacial areas of the Southern Alps that were collected over a period of approximately four decades from 1977 to 2014 were analysed to evaluate the impact of environmental traits on the distribution of chironomid species. Although the list of species has not substantially changed over time, some rare species captured in the 1970s have not been collected in recent years, while other species have only been collected recently. 2. The recovered correlation between altitude of the sampling sites and the date of collection since the first sampling event emphasises the need, in recent years, to sample at higher altitudes to collect species living near the glacier snout. This result confirms the impact of glacial retreat on chironomid communities. 3. Temporal trends in diversity were not emphasised throughout the collecting period. 4. A canonical correspondence analysis (CCA) showed that the influence of glaciers is the ecological trait that is the most robust predictor of the spatial distribution of species. This trait was highly correlated with the first CCA axis. Diamesa steinboecki, Diamesa latitarsis, Diamesa modesta, Diamesa goetghebueri and Diamesa laticauda are species that are known to be restricted to glacial habitats and were correlated with the first axis. The second CCA axis separated Western from Central-Eastern glaciers, with Diamesa cinerella prevailing in the former. 5. The threshold indicator taxa analysis, which detects changes in the distribution of taxa along an environmental gradient, confirmed the results of CCA in selecting Diamesa species with the strongest preference for glacial habitats.