Untangling island biogeography of terrestrial vertebrates in protected areas of America

Island Biogeography Theory (IBT) is a foundational framework in conservation science, yet its application to large-scale protected area (PA) design remains relatively understudied. This research investigates the influence of IBT-derived variables on terrestrial vertebrate richness and threatened species abundance within 4990 PAs across continental America. By examining the effects of area, shape, isolation, elevation, latitude, and human influence, we assessed the relative importance of these factors in shaping vertebrate diversity patterns. Our findings reveal that while IBT principles, such as the positive relationship between area and species richness, are evident, the influence of human activities is pervasive. Specifically, latitude and elevation significantly influenced species richness for most taxonomic groups, while area positively affected amphibians, birds, reptiles, and threatened mammals and reptiles. Shape and isolation exhibited varying degrees of impact across different taxa. Critically, human influence emerged as a dominant factor, particularly for birds, including threatened species. These results underscore the complex interplay between natural and anthropogenic processes in shaping biodiversity patterns. To effectively conserve terrestrial vertebrates, and overall biodiversity, PA managers and policy-makers must integrate IBT principles with strategies that address the impacts of human activities, such as habitat loss, fragmentation, and climate change.