Data Bruschini et al.

The Mediterranean region is at the same time a biodiversity and a climate change hotspot, with forecasted increased summer aridity. In Northern Europe, butterflies generally expand their distribution poleward, while this dynamic does not result in population loss at Southern Mediterranean boundaries. This suggests the existence of mechanisms to cope with increasing aridity and their identification will be key to tailoring data-driven conservation strategies. We examined the fine-scale dynamics of butterfly species in the Mediterranean hills (~900m a.s.l.) of the Monte Peglia UNESCO reserve (Central Italy). We fortnightly sampled 90 plots from April to October 2022 (the locally hottest summer of the last 10 years) and documented three main patterns: 1) butterfly richness and abundance correlate with environmental features and these relationships vary across seasons. Richer sites consisted of some 30% of woods coverage and were located at higher altitudes and closer to water during summer (area-based analysis). 2) Environmental preferences vary according to species traits. Specialist species and those adapted to colder climates and narrower temperature ranges were more abundant in sites at higher altitudes, closer to water bodies and with wider woodland coverage (fourth-quadrant analysis). 3) Although most species preferred meadow habitats, when temperature increases, they were more abundant in sites with wider tree coverage, closer to streams, and at higher altitude (species-based analysis). This dynamic demonstrates that butterflies opportunistically move to cooler micro-habitats to buffer high temperatures. This phenomenon potentially involves most of the community since the species showing significant effects encompass >80% of the observed individuals. Our results introduce new dimensions to the niche of Mediterranean butterflies, highlighting the importance of shady micro-habitats, altitudinal ranges, and water streams, which will likely to become critical with increased aridity. By combining our results with literature data, we provided a protocol to preserve Mediterranean butterflies within the resist-accept-direct framework.