气候变化预计会改变很多动物和植物物种的地理分布范围，包括它们所处环境的纬度和海拔。然而，很多所报道的分布范围变化都很特殊，即便在分类上相似的物种中也是如此，一个物种分布范围的纬度或海拔低限未必同其高限移动得一样快。
Daniel Doak 和 William Morris利用关于冻原植物“无茎麦瓶草”和“高山比斯托草”的种群统计数据发现，在低限上所发生的种群变化速度补偿气候变暖，但这种效应不会持久，当温度再升高时就会达到一个顶点（引爆点）。
推荐英文摘要：
Nature doi:10.1038/nature09439
Demographic compensation and tipping points in climate-induced range shifts
Daniel F. Doak1,3 " William F. Morris2,3
1Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming 82071, USA
2Biology Department, Duke University, Box 90338, Durham, North Carolina 27708, USA
3These authors contributed equally to this work.
To persist, species are expected to shift their geographical ranges polewards or to higher elevations as the Earth’s climate warms1, 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 contractions5, 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 detrimental, as most demographic rates that improved in moderately warmer years declined in the warmest years, with the potential to drive future population declines. Our results emphasize the need for long-term, range-wide measurement of all population processes to detect demographic compensation and to identify nonlinear responses that may lead to sudden range shifts as climatic tipping points are exceeded.
