Background/Question/Methods   Here we examine patterns of butterfly species richness among groups differing in degree of specialization and mobility in the north-west Mediterranean Basin, a European hotspot for this taxon. To model butterfly richness, we use precise data on the composition of a large number of butterfly communities, correct for spatial autocorrelation and take into consideration the main potential drivers that include climatic, geographic and resource variables, as well as landscape structure and human environmental impact at different spatial scales.

Results/Conclusions   Our study shows that climatic and anthropogenic factors play an important role in determining butterfly species richness in the north-west Mediterranean Basin. Water availability, a product of the interplay between temperature and rainfall, appears as the most determinant factor. Maximum diversity was observed at mid-altitudes, which reveals the importance from a conservation point of view of Mediterranean mountain ranges. The results suggest serious population declines in specialist species restricted to mountain areas as a result of climate warming in combination with habitat loss caused by the abandonment of grazing and mowing. They also suggest negative trends for generalist species due to an increase in aridity in combination with an increase in intensification of human land use in lowland areas. Such synergies are expected to lead to rapid declines in Mediterranean butterfly populations in the coming years, thereby posing a severe threat for the conservation of European biodiversity.