Johnston Aaron N, Christophersen Roger G, Beever Erik A, Ransom Jason I
U. S. Geological Survey Northern Rocky Mountain Science Center Bozeman MT USA.
School of Environmental and Forest Sciences University of Washington Seattle WA USA.
Ecol Evol. 2020 Dec 29;11(3):1264-1279. doi: 10.1002/ece3.7126. eCollection 2021 Feb.
Recent snow droughts associated with unusually warm winters are predicted to increase in frequency and affect species dependent upon snowpack for winter survival. Changes in populations of some cold-adapted species have been attributed to heat stress or indirect effects on habitat from unusually warm summers, but little is known about the importance of winter weather to population dynamics and how responses to snow drought vary among sympatric species. We evaluated changes in abundance of hoary marmots () over a period that included a year of record-low snowpack to identify mechanisms associated with weather and snowpack. To consider interspecies comparisons, our analysis used the same a priori model set as a concurrent study that evaluated responses of American pikas () to weather and snowpack in the same study area of North Cascades National Park, Washington, USA. We hypothesized that marmot abundance reflected mechanisms related to heat stress, cold stress, cold exposure without an insulating snowpack, snowpack duration, atmospheric moisture, growing-season precipitation, or select combinations of these mechanisms. Changes in marmot abundances included a 74% decline from 2007 to 2016 and were best explained by an interaction of chronic dryness with exposure to acute cold without snowpack in winter. Physiological stress during hibernation from exposure to cold, dry air appeared to be the most likely mechanism of change in marmot abundance. Alternative mechanisms associated with changes to winter weather, including early emergence from hibernation or altered vegetation dynamics, had less support. A post hoc assessment of vegetative phenology and productivity did not support vegetation dynamics as a primary driver of marmot abundance across years. Although marmot and pika abundances were explained by strikingly similar models over periods of many years, details of the mechanisms involved likely differ between species because pika abundances increased in areas where marmots declined. Such differences may lead to diverging geographic distributions of these species as global change continues.
预计与异常温暖冬季相关的近期雪灾干旱频率将会增加，并影响依赖积雪过冬的物种。一些适应寒冷环境的物种数量变化被归因于热应激或异常温暖夏季对栖息地的间接影响，但对于冬季天气对种群动态的重要性以及同域物种对雪灾干旱的反应差异，人们了解甚少。我们评估了在一段包括创纪录低积雪年份的时期内，灰白旱獭（）数量的变化，以确定与天气和积雪相关的机制。为了进行种间比较，我们的分析使用了与一项同期研究相同的先验模型集，该研究评估了美国鼠兔（）对美国华盛顿州北卡斯卡德国家公园同一研究区域内天气和积雪的反应。我们假设旱獭数量反映了与热应激、冷应激、没有绝缘积雪时的冷暴露、积雪持续时间、大气湿度、生长季降水或这些机制的特定组合相关的机制。旱獭数量的变化包括从2007年到2016年下降了74%，最好的解释是长期干旱与冬季无积雪时的急性寒冷暴露之间的相互作用。冬眠期间暴露于寒冷、干燥空气中所产生的生理应激似乎是旱獭数量变化最可能的机制。与冬季天气变化相关的其他机制，包括冬眠提前结束或植被动态改变，得到的支持较少。对植物物候和生产力的事后评估并不支持植被动态是多年来旱獭数量的主要驱动因素这一观点。尽管在多年时间里，旱獭和鼠兔数量由惊人相似的模型解释，但由于在旱獭数量下降的地区鼠兔数量增加，所涉及机制的细节在物种之间可能有所不同。随着全球变化的持续，这种差异可能导致这些物种的地理分布出现分歧。
