Elevated human footprint on islands promotes both introduction and extinction probability of insular reptiles at opposite ends of geographic, evolutionary and ecological continua

Abstract

AbstractThe Anthropocene is marked by unprecedented changes to species ranges worldwide. Introduced species expand their native range into new geographic regions while extinction-prone species experience severe native range contraction. Introductions and extinctions are both caused by how species respond to human influence within their native ranges. The question arises if the opposite response in distributional change is due to introduced and extinction-prone species falling at opposite ends of geographic, evolutionary and ecological trait continua. Here, we assess the factors that explain the introduction and extinction-prone status for 3111 squamate reptile species native to the western hemisphere, of which 142 species have been introduced elsewhere and 483 species are threatened with extinction. We first asked what geographic regions contained the most introduced and extinction-prone species and if these species are evolutionarily related. We then tested the opposite ends hypothesis for several species characteristics. Our results show that the native ranges of introduced and extinction-prone reptiles are skewed towards island regions and that significant phylogenetic signal exists for these two groups, indicating they are not a random selection of the reptiles that have evolved in the western hemisphere. Species whose native ranges were more insular and were more influenced by humans were more likely to be introduced or extinction-prone. Evolutionary factors did not explain species status, but multiple geographic and ecological factors supported the opposite ends hypothesis. Introduced species were positively associated with herbivory and omnivory and had large and complex ranges, whereas extinction-prone species were generally carnivorous with small and simple ranges. In addition, introduced species produced larger clutches and extinction-prone species had relatively small body sizes. In the Anthropocene, the naive ranges of introduced and extinction-prone species are situated in the same human-impacted regions, but species range characteristics and functional traits determine whether species ranges expand or contract in the continuing face of global change.