Contrasting and altitude‐specific temporal trends in functional, phylogenetic, and species diversity in Austrian butterfly communities

Climate change and anthropogenic alteration of landscapes negatively impact the abundance and species diversity of plant and animal communities worldwide. Much less is known about the effects on phylogenetic diversity and community functioning. Here we use long‐term butterfly data (1980–2022) from the Austrian Alps along an elevation gradient. We assessed how communities adjust structures and functionality to increasing temperatures, and how these changes are linked to trait expression and community functioning. Species diversity decreased at low and intermediate altitudes, and increased at high ones. Functional diversity was lower than expected by a random model at intermediate and high altitudes and increased with time at high, but not at intermediate and low altitudes. Phylogenetic diversity did not show significant temporal trends at low altitude, but increased with time at intermediate and high altitudes. Multifunctionality significantly decreased at intermediate and high altitudes and was not significantly correlated with functional diversity, but was negatively correlated with phylogenetic diversity. We argue that the ongoing homogenisation of Alpine butterfly communities strongly affects species, functional and phylogenetic diversity. The assessment of species richness and diversity alone, as provided by common species surveys, might give a false impression about the state and functional diversity of Alpine insect communities in the course of climate change. The directions of faunal changes heavily depend on altitude and therefore on specific climatic conditions. Higher altitudes face decreasing butterfly multifunctionality despite of increasing species richness due to climate induced altitudinal up‐hill shifts of many species. We conclude that studies on community time series should include phylogenetic and functional diversity besides of being focused on richness and endangerment. Red lists might be extended by categories on functional importance and phylogenetic distinctness.