Independent Researcher, P.O. Box 1431, Greeley, Colorado, 80632, USA.
Environmental Studies Program, University of Colorado Boulder, 4001 Discovery Drive, Boulder, Colorado, 80309, USA.
Ecology. 2017 Apr;98(4):1071-1081. doi: 10.1002/ecy.1738. Epub 2017 Mar 20.
The mechanisms that stabilize small populations in the face of environmental variation are crucial to their long-term persistence. Building from diversity-stability concepts in community ecology, within-population diversity is gaining attention as an important component of population stability. Genetic and microhabitat variation within populations can generate diverse responses to common environmental fluctuations, dampening temporal variability across the population as a whole through portfolio effects. Yet, the potential for portfolio effects to operate at small scales within populations or to change with systematic environmental shifts, such as climate change, remain largely unexplored. We tracked the abundance of a rare alpine perennial plant, Saussurea weberi, in 49 1-m plots within a single population over 20 yr. We estimated among-plot correlations in log annual growth rate to test for population-level synchrony and quantify portfolio effects across the 20-yr study period and also in 5-yr subsets based on June temperature quartiles. Asynchrony among plots, due to different plot-level responses to June temperature, reduced overall fluctuations in abundance and the probability of decline in population models, even when accounting for the effects of density dependence on dynamics. However, plots became more synchronous and portfolio effects decreased during the warmest years of the study, suggesting that future climate warming may erode stabilizing mechanisms in populations of this rare plant.
面对环境变化而稳定小种群的机制对其长期生存至关重要。基于群落生态学中的多样性-稳定性概念，种群内多样性作为种群稳定性的一个重要组成部分受到了关注。种群内的遗传和微生境变异可以产生对常见环境波动的多样化响应，通过投资组合效应缓冲整个种群的时间变异性。然而，投资组合效应在种群内小尺度上运作的潜力或随着系统环境变化（如气候变化）而变化的潜力在很大程度上仍未得到探索。我们在 20 年内跟踪了一个单一种群中 49 个 1 平方米的斑块内一种稀有高山多年生植物——雪莲的丰度。我们估计了对数年度增长率的斑块间相关性，以检验种群水平的同步性，并在 20 年的研究期间以及基于 6 月温度四分位数的 5 年子集中量化投资组合效应。由于不同斑块对 6 月温度的不同反应，斑块间的不同步性降低了丰度的总体波动，并降低了种群模型中衰退的概率，即使考虑了密度依赖性对动态的影响。然而，在研究中最温暖的年份，斑块变得更加同步，投资组合效应降低，这表明未来气候变暖可能会侵蚀这种稀有植物种群的稳定机制。
