Island incidence and mainland population density: Mammals from Mediterranean islands

Abstract

The reasons why some species are resistant to extinction or are better invaders of islands than others remain unexplained. In this study, we test the hypothesis that mammals living on the mainland at higher density than predicted by the density/body mass relationship have a much greater chance to colonize a small island successfully, and/or that they are less likely to become extinct when living on small islands. For this, we used data compiled on mammals from a number of Mediterranean islands. We show a nested pattern for mammals on western Mediterranean islands, which suggests that the distribution of mammals on these islands is not the result of a random process. Using two comparative methods, we show that mammal density on the mainland, corrected for body mass, is negatively correlated with island size. Mammals with a high density compared to the density/mass relationship are the best invaders and/or probably have less chance of going extinct on small islands when population size is small.