Reptile Extinctions on Land-Bridge Islands: Life-History Attributes and Vulnerability to Extinction

One of the central questions of conservation biology is what life-history traits render a species prone to extinction. We addressed this problem by calculating extinction rates for 35 species of turtles and squamates (lizards and snakes) occurring on 87 land-bridge islands in the Mediterranean Sea. We calculated extinction rates in two ways: first, by incorporating the known sequence of historical island separations and second by ignoring history and assuming that the islands became isolated simultaneously. The second procedure is simpler and more frequently used in the literature and produces estimates of extinction rates that are similar to the first, more complex procedure. We then determined the relationship between extinction rates (calculated using both methods) and body mass, longevity, habitat specialization, and population abundance using two methods: first, by accounting for the phylogenetic relationships among species and, second, by ignoring them. Only population abundance and habitat specialization explained a significant amount of the observed variation in species extinction rates. Body mass itself did not explain variation in extinction rates, although it was strongly correlated with abundance. These conclusions were obtained using both procedures for calculating extinction rates and both procedures for correlating extinction rates with life-history traits.