Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming 82071, USA.
Nature. 2010 Oct 21;467(7318):959-62. doi: 10.1038/nature09439.
To persist, species are expected to shift their geographical ranges polewards or to higher elevations as the Earth's climate warms. 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. 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.
为了生存，物种预计将随着地球气候变暖而向极地或高海拔地区转移。然而，尽管许多物种的分布范围在历史时期已经发生了变化，但许多其他物种并没有发生变化，或者只在高纬度或高海拔地区发生了变化，导致了分布范围的扩大而不是缩小。鉴于这些对气候变暖的特殊反应及其对物种对气候变化脆弱性的不同影响，一个关键任务是了解为什么有些物种没有改变它们的分布范围，特别是在赤道或低海拔地区，以及随着气候变暖的持续，这种弹性是否会持续下去。在这里，我们表明，人口增长率的补偿性变化正在缓冲北美两种苔原植物的南部种群免受气候变暖的负面影响，减缓了它们向北方的分布转移，但这种缓冲不太可能无限期地持续下去。这两个物种的南部种群的存活率和繁殖率较低，但个体植物的生长率较高，可能是由于较长、较温暖的生长季节。由于这些和其他补偿性变化，南部种群的人口增长率目前并不低于北部种群。然而，持续的变暖可能仍然是有害的，因为在较温暖的年份中改善的大多数人口增长率在最温暖的年份中下降了，这有可能导致未来的人口下降。我们的研究结果强调了需要对所有种群过程进行长期的、广泛的测量，以检测人口补偿，并识别可能导致气候临界点超过时突然发生分布范围转移的非线性反应。
