Influence of Recent Geography and Paleogeography on the Structure of Reptile Communities in a Land-Bridge Archipelago

The herpetofauna of the Tuscan Islands (Central Italy) is well known and represents an ideal subject to understand the role of current and historical factors responsible for biogeographical patterns in a complex archipelago. Multidimensional Scaling, cluster analyses, species-area relationships, Mantel tests and co-occurrence statistics were used to investigate the influence of current geography and Pleistocene connections with the mainland on the structure of insular communities. Although reptile colonization likely occurred via land bridges for islands that were connected to the mainland in the Pleistocene, a long time relaxation (species extinction by island habitat loss after disconnection and new colonization by over sea dispersal or human-assisted introductions) equilibrated the faunas according to island area. Biogeographical similarities among islands increased for islands located farther from Corsica and Tuscany, thus suggesting that, for remote islands, interisland faunal exchanges occurred more frequently than mainland-island colonization. Also, a possible influence of Pleistocene geography emerged more clearly when populations suspected to be introduced by man were removed. Co-occurrence analyses indicated a nonrandom distribution influenced by island area and distance, suggesting that the time elapsed since post-Pleistocene disconnection may have reshaped biogeographical similarities by an increase in competition resulting from reduction in island areas and introduction of certain species. From a conservation viewpoint, the land-bridge distribution of organisms with poor mobility should be carefully considered in conservation biogeography, because depletion of island populations cannot be balanced by new immigrations from the mainland, whereas introduction of nonnative species may have a negative impact on the original fauna.