The James Hutton Institute, Aberdeen, AB15 8QH, UK.
Natural History Museum, University of Oslo, Box 1172 Blindern, NO-0318, Oslo, Norway.
Glob Chang Biol. 2017 Apr;23(4):1374-1389. doi: 10.1111/gcb.13435. Epub 2016 Aug 6.
The cumulative effects of climate warming on herbivore vital rates and population dynamics are hard to predict, given that the expected effects differ between seasons. In the Arctic, warmer summers enhance plant growth which should lead to heavier and more fertile individuals in the autumn. Conversely, warm spells in winter with rainfall (rain-on-snow) can cause 'icing', restricting access to forage, resulting in starvation, lower survival and fecundity. As body condition is a 'barometer' of energy demands relative to energy intake, we explored the causes and consequences of variation in body mass of wild female Svalbard reindeer (Rangifer tarandus platyrhynchus) from 1994 to 2015, a period of marked climate warming. Late winter (April) body mass explained 88% of the between-year variation in population growth rate, because it strongly influenced reproductive loss, and hence subsequent fecundity (92%), as well as survival (94%) and recruitment (93%). Autumn (October) body mass affected ovulation rates but did not affect fecundity. April body mass showed no long-term trend (coefficient of variation, CV = 8.8%) and was higher following warm autumn (October) weather, reflecting delays in winter onset, but most strongly, and negatively, related to 'rain-on-snow' events. October body mass (CV = 2.5%) increased over the study due to higher plant productivity in the increasingly warm summers. Density-dependent mass change suggested competition for resources in both winter and summer but was less pronounced in recent years, despite an increasing population size. While continued climate warming is expected to increase the carrying capacity of the high Arctic tundra, it is also likely to cause more frequent icing events. Our analyses suggest that these contrasting effects may cause larger seasonal fluctuations in body mass and vital rates. Overall our findings provide an important 'missing' mechanistic link in the current understanding of the population biology of a keystone species in a rapidly warming Arctic.
鉴于预期的影响因季节而异，气候变暖对食草动物生命关键指标和种群动态的累积影响难以预测。在北极，温暖的夏季促进了植物生长，这应该会导致秋季个体更重、更肥沃。相反，冬季温暖的融雪天气（雨夹雪）会导致“结冰”，限制了对饲料的获取，导致饥饿、存活率降低和繁殖力下降。由于身体状况是衡量能量需求与能量摄入之间关系的“晴雨表”，我们在 1994 年至 2015 年期间探索了气候变化期间野生雌性斯瓦尔巴驯鹿（Rangifer tarandus platyrhynchus）体重变化的原因和后果，这是一个气候明显变暖的时期。早春（4 月）体重解释了种群增长率的 88%的年际变化，因为它强烈影响生殖损失，从而影响随后的繁殖力（92%）、存活率（94%）和补充率（93%）。秋季（10 月）体重会影响排卵率，但不影响繁殖力。4 月体重没有长期趋势（变异系数，CV=8.8%），在温暖的秋季（10 月）后体重更高，反映了冬季开始的延迟，但与“雨夹雪”事件的关系最为强烈和负面。10 月体重（CV=2.5%）随着研究的进行而增加，这是由于越来越温暖的夏季植物生产力提高。密度依赖的质量变化表明冬季和夏季资源竞争，但近年来由于种群规模不断增加，竞争程度并不明显。虽然预计持续的气候变暖将增加高北极苔原的承载能力，但也可能导致更频繁的结冰事件。我们的分析表明，这些相反的影响可能会导致体重和生命关键指标的季节性波动更大。总的来说，我们的研究结果提供了一个重要的“缺失”的机制联系，当前对快速变暖的北极关键物种的种群生物学的理解。
