Biogeography of Terrestrial Gastropods of North-West Spain

Abstract

We carried out a biogeographical study of the terrestrial gastropods of north-west Spain on the basis of sampling from 51 10 X 10 km quadrants in the regions of Asturias, Leon, Zamora and Salamanca. Classification of quadrants by species composition using indicator species analysis (program TwINsPAN) revealed a zonation which corresponds very closely to the phytoclimatic zonation developed by Rivas Martinez. Correspondence analysis (program cANoco), using nominal environmental variables, confirmed the TWINSPAN classification and allowed identification of those factors which are most important in determining the broad patterns of terrestrial gastropod distribution in north-west Spain. The region corresponding to Rivas Martinez's Eurosiberian region is characterized by mean annual precipitation in excess of 700 mm and high gastropod species richness; that corresponding to Rivas Martinez's Mediterranean region is characterized by mean annual precipitation below 700 mm and a lower gastropod species richness. It is also of interest that the Eurosiberian part of our study area is an older landmass (having emerged in the Palaeozoic) than the Mediterranean part (which emerged in the Mesozoic and Cenozoic).