Demographic compensation and tipping points in climate-induced range shifts

Chasing the climate Climate change is expected to shift the geographical ranges of many animal and plant species, in terms of both the latitude and altitude of their habitat. Many reported range shifts have been idiosyncratic, however, even among taxonomically similar species, with the low latitude or low altitude limit of a species' range not necessarily moving as fast as the high edge. Using demographic data on the tundra plants moss campion and alpine bistort, Daniel Doak and William Morris show that changed demographic rates at the lower edge are compensating for the warming climate, but that this effect will not last and a tipping point may be reached as temperatures get warmer. Climate change is expected to shift the latitudinal and altitudinal ranges of species, but the low latitude or low altitude edge does not necessarily move as fast as the high edge. Here, demographic data on two tundra plants have been used to show that changed demographic rates at the lower edge are compensating for the warming climate, but that this effect will not last and a tipping point will be reached as temperatures get warmer. To persist, species are expected to shift their geographical ranges polewards or to higher elevations as the Earth’s climate warms 1 , 2 , 3 , 4 . However, although many species’ ranges have shifted in historical times, many others have not, or have shifted only at the high-latitude or high-elevation limits, leading to range expansions rather than contractions 5 , 6 , 7 , 8 , 9 , 10 , 11 . Given these idiosyncratic responses to climate warming, and their varied implications for species’ vulnerability to climate change, a critical task is to understand why some species have not shifted their ranges, particularly at the equatorial or low-elevation limits, and whether such resilience will last as warming continues. Here we show that compensatory changes in demographic rates are buffering southern populations of two North American tundra plants against the negative effects of a warming climate, slowing their northward range shifts, but that this buffering is unlikely to continue indefinitely. Southern populations of both species showed lower survival and recruitment but higher growth of individual plants, possibly owing to longer, warmer growing seasons. Because of these and other compensatory changes, the population growth rates of southern populations are not at present lower than those of northern ones. However, continued warming may yet prove detr