IMPORTANCE OF HISTORICAL FACTORS ON SPECIES RICHNESS AND COMPOSITION OF BUTTERFLY ASSEMBLAGES (LEPIDOPTERA, RHOPALOCERA) IN A NORTHERN IBERIAN MOUNTAIN-RANGE

The butterfly assemblages of three vegetation types (pasture, heathlan d and rocky outcrop with Genista spp.) and two geographical orientatio ns (a northern slope and a sheltered gorge) were studied along an alti tudinal gradient in the Picos de Europa in northern Spain. In order to study the effects of historical climatic changes on current butterfly assemblages, it was examined if changes in richness and faunal compos ition of assemblages were joined with changes in their biogeographical composition. The three vegetation types showed characteristic butterf ly assemblages, but no difference in species richness and biogeographi cal composition was found. Species richness in the sheltered gorge was higher than in the northern slope. Faunal composition also varied bet ween orientations and there were more widespread and Mediterranean spe cies in the sheltered gorge than in the northern slope. Species richne ss declined with increasing altitude, though a mid-altitudinal peak wa s observed. There was a faunal segregation between high and low locali ties. Species richness of widespread and Mediterranean butterflies dec reased as altitude increased, whereas the reverse was true for montane species. Moreover, biogeographical elements differed in their climati c tolerances measured as altitudinal ranges. Therefore, changes in ric hness and composition of butterfly assemblages between both slopes and along the altitudinal gradient were joined in part with variation in their biogeographical composition. These results suggest that current species richness and composition of butterfly assemblages in the Picos de Europa might be the consequence of differential colonization of re fuges during the past climatic changes.