Functional semelparity drives population dynamics and endangers a peripheral population

Despite increased risk of extinction through stochastic events, peripheral populations are conservation priorities as the distribution of endangered species tends to contract to the periphery of historic ranges rather than toward the core. Trailing-edge populations and mountain isolates, which may become more common as climate change drives range shifts, are an important realm of inquiry and contain important reserves of genetic variation. We use long-term monitoring data from the southernmost population of a widespread species to test the hypothesis that peripheral populations display distinct demographic profiles from core populations. The red squirrel (Tamiasciurus hudsonicus) is predicted to recede from its southern border in response to climate-induced habitat change. We estimate key demographic parameters for this endangered population using survival and reproduction schedules and compare the dynamics to core populations of this and related species. This peripheral population exhibits higher adult mortality, and suffers associated impacts on reproductive output, which results in a demography distinct from core populations and phylogenetically similar species. Poor adult survival, similar to a population that experiences extremely high hunting pressure, has resulted in this normally iteroparous species becoming functionally semelparous at the periphery. Understanding differences in demographic function between peripheral and core populations is key if management strategies are to be effective in supporting continued persistence of at risk populations in the face of range shifts of species or habitats driven by environmental change.