The great acceleration of island saturation by species introductions in the Anthropocene has altered species-area relationships

Abstract

AbstractThe species-area relationship (SAR) is a fundamental pattern of island biogeography which is often curvilinear due to reduced accumulation of species on mid-sized island caused by island isolation and the lack of speciation present on larger islands. The curvature of SARs represents lower saturation of species on mid-sized islands and therefore accelerated species accumulation should linearize island SARs. In the Anthropocene, island species accumulation has accelerated from introduced species. We hypothesize three new patterns. First, the saturation of species for the most unsaturated islands should increase more from introduced species than other islands. Second, SARs should become more linear as islands accumulate more species. Third, introduced species should greatly accelerate the island saturation process. We assessed these patterns for the reptile and amphibian of the Caribbean, a global hotspot of biodiversity. Mid-sized Caribbean islands are now more saturated causing a linearization of contemporary herpetofauna SARs resulting from a ca. 30 myr and 40 myr acceleration of island saturation for reptiles and amphibians, respectively. Thus, humans within the last few hundreds of years—starting with European colonization of the Americas—have greatly accelerated the natural process of island saturation by 30 million years within the Caribbean global biodiversity hotspot.