Mountains occupy around 25% of Earth’s land but they hold disproportionate amounts of biodiversity. Southwestern European mountain ranges harbour one of the highest butterfly biodiversity of the continent, but they have not been extensively long-term monitored due to the difficult terrain and weather conditions. Nowadays, the abandonment of traditional land uses is giving rise to a succession towards forest habitats in these mountains. Coupled to these land use changes, climate change is predicted to severely affect mountain ecosystems.
The general aim of this thesis was to investigate the conservation status of butterflies at Picos de Europa National Park (NW Spain). Overall, we found a rapid decline both on total butterfly numbers and for individual species populations: 45% of butterfly abundance lost and species richness and Shannon diversity declining in the last 14 years. Moreover, 26% of species with sufficient data to assess population trends, showed a significant negative population trend. Using multispecies abundance indicators allowed us to identify the drivers of those declines, with the advance of forests over grasslands due to rural abandonment and warming most likely to be responsible for the decline and re-organisation of butterfly communities. We found an annual increase of mean temperature in the study area of 0.021 ºC in the period 1979-2019, representing an increase of 0.21ºC per decade in the last 40 years. We also explored the patterns of butterfly diversity along elevation, which peaked twice, at lower (150 m) and intermediate elevations (1500 m), and identified the environmental drivers of those patterns. Butterfly diversity was positively affected by near-surface relative humidity and continentality. Butterfly communities composition was affected by abandonment, with a species turnover of 48% after 18 years. Species with higher preference for closed habitats increased their densities as time since abandonment proceeded.
Land abandonment and amplified effects of climate change are acting upon other mountain ranges in Europe (Pyrenees, Carpathian mountains, Balkan mountains and the Alps, among many others). More focus is needed on mountain ecosystems, biodiversity and cultural hotspots, that are undergoing accelerated major changes.