Recent increasing homogenisation in Austrian butterfly communities over the past decades

In Europe, abundance, biomass and species richness of many insect taxa declined during the last decades. This decline might be accompanied by long-term temporal changes in community composition and dominance orders. Here, we use the data base of the natural history museum of Salzburg based on museum records and field books on Austrian butterflies covering the years 1945-2018 and asked 1) whether and how community composition of important butterfly guilds changed and 2) whether these changes are in accordance with reciprocal shifts in species abundances leading to increased functional stability. In comparisons of annual changes in dominance orders, we found an increasing tendency of compositional stability of dominant species. The trend was most pronounced in generalist and dispersive species, while dominant grassland, xerothermophilic and sedentary species tended to decrease in relative abundance. We also demonstrate a temporal trend towards increasing regional stability in relative abundance rank orders. We did not find compelling evidence for reciprocal shifts in abundances of dominant and subdominant species of the same guild and of asynchronous population fluctuations as required by models that link abundance compensation and functional stability. Our study highlights the ongoing trend towards faunal homogenisation at regional spatial scales in the European Alps.