Identifying global hotspots of avian trailing-edge population diversity

Abstract

Climate change is causing the ranges of many species to shift poleward and to higher elevations. Trailing-edge populations near the low-latitude edge of a shifting range are predicted to be at high risk of climate-induced extinction, but conservation efforts are hindered by a lack of information about the global distribution of trailing-edge populations. We used a large spatial dataset on the ranges of nearly all extant avian species to identify potential hotspots where trailing-edge populations represent a large proportion of the total avifauna. We identified potential trailing-edge population hotspots by isolating and overlaying low latitude regions of species’ ranges, and computing the proportion of total species richness in a location comprised of low-latitude populations. We identified potential hotspots on all continents other than Antarctica. Potential trailing-edge population diversity was highest near the equator, low-latitude margins of mountain ranges, desert edges, and along coastlines. Because a potential trailing-edge population hotspot might not be an actual trailing-edge population hotspot if the low-latitude populations are not declining, information on population trends is necessary for confirmation. As a case study, we focused on one of the identified hotspots, the Southern Appalachian Mountains, where our analysis indicated that 30 bird species have potential trailing-edge populations. Even though more population studies have been conducted in the Appalachian Mountains than in most of the other potential hotspots that we identified, there was insufficient information available from the high elevations where these species occur to make strong inferences about population declines. Our research highlights the need for a concerted effort to gather more information about population trends in the regions we identified as potential hotspots of trailing-edge population diversity.