Island characteristics and species traits predict mammal diversity across islands of the great lakes of North America

Island biogeography theory states biodiversity increases with island size and decreases with distance from mainland source populations; however, the influence of other island characteristics (e.g., presence of neighboring islands) and species traits (e.g., body size) could alter expected patterns. We assessed the influence of island characteristics and species traits on island biodiversity using presence data for 20 mammal species on 70 islands across the Great Lakes of North America. We collated presence data from public databases of species distributions, a literature review, and personal communications with resource managers and researchers. As predicted, islands closer to mainland source populations as well as islands and archipelagoes with larger areas supported greater mammalian species richness. Winter dormant species (e.g., American black bear [ Ursus americanus ]) occurred less on islands while semiaquatic species (e.g., American beaver [ Castor canadensis ]) occurred more. Our results broadly support island biogeography theory and highlight the importance of considering archipelago characteristics and species traits for describing island biodiversity. Specifically, we found support for the existence of archipelagic meta-communities whereby archipelago area was a better predictor of mammalian species richness than the area of individual islands and further support for the effects of winter dormancy and semiaquatic lifestyles as species traits predictive of mammal occurrence on islands. Our results may aid restoration and conservation planning including consideration of assisted colonization and invasive species precautions. Further, our dataset provides an important baseline for mammal diversity and distributions in the Great Lakes region.