Chloé Schmidt , Jussi Mäkinen, Jean-Philippe Lessard , Colin J Garroway

Changing species distributions due to global change underscore a pressing need to better understand range limits. However, our knowledge of general determinants of range limits remains poor despite over a century of work. Theoretical models demonstrate that genetic drift should strengthen across environmental gradients. This can limit natural selection to the point where populations can no longer adapt to new conditions and range edges form. How widely this theory holds in real-world populations is uncertain. With data comprising 37,397 genotypes sampled across the ranges of 59 mammal species, we found support for a central role of genetic drift-imposed limits to selection in setting range limits. While range limits are often considered in terms of environmental tolerances at the species level, the efficiency of selection is limited at the population level. This can explain idiosyncratic patterns of range expansion and collapse due to climate change and human land use.