Area, isolation, and climate explain the diversity of mammals on island worldwide

Identifying the determinants of insular biodiversity at large scales remains a question in biogeography. We conducted a global test of island biogeography theory by evaluating the importance of island physical, environmental, and historical characteristics on mammal species richness and endemism. We quantified the effects of island characteristics while accommodating variation among biogeographic realms by fitting generalized linear and mixed models. Analyzes were also performed separately for bats and non-volant mammals. Diversity patterns were most consistently influenced by the physical characteristics of the islands. Area positively affected mammal diversity, in particular the number of non-volant endemics. Island isolation, both current and past, was associated with lower richness but greater endemism. Flight capacity modified the relative importance of past versus current isolation, with bats responding more strongly to current and non-volant mammals to past isolation. Environmental effects on biodiversity were more variable, with a tendency for greater effects on endemism than on richness. Unexpectedly, climate change velocity was positively associated with endemism. In line with island biogeography theory, we found that area and isolation were among the strongest drivers of overall mammalian biodiversity. Moreover, our results support the growing evidence on the importance of past conditions on current patterns, particularly on non-volant species.