Earth to Ocean Research Group, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, V5K 4B2, Canada.
Conservation Science Partners, 11050 Pioneer Trail, Suite 202, Truckee, California, 96161, USA.
Ecol Appl. 2019 Mar;29(2):e01832. doi: 10.1002/eap.1832. Epub 2018 Dec 27.
Anthropogenic climate change presents challenges and opportunities to the growth, reproduction, and survival of individuals throughout their life cycles. Demographic compensation among life-history stages has the potential to buffer populations from decline, but alternatively, compounding negative effects can lead to accelerated population decline and extinction. In montane ecosystems of the U.S. Pacific Northwest, increasing temperatures are resulting in a transition from snow-dominated to rain-dominated precipitation events, reducing snowpack. For ectotherms such as amphibians, warmer winters can reduce the frequency of critical minimum temperatures and increase the length of summer growing seasons, benefiting post-metamorphic stages, but may also increase metabolic costs during winter months, which could decrease survival. Lower snowpack levels also result in wetlands that dry sooner or more frequently in the summer, increasing larval desiccation risk. To evaluate how these challenges and opportunities compound within a species' life history, we collected demographic data on Cascades frog (Rana cascadae) in Olympic National Park in Washington state to parameterize stage-based stochastic matrix population models under current and future (A1B, 2040s, and 2080s) environmental conditions. We estimated the proportion of reproductive effort lost each year due to drying using watershed-specific hydrologic models, and coupled this with an analysis that relates 15 yr of R. cascadae abundance data with a suite of climate variables. We estimated the current population growth (λ ) to be 0.97 (95% CI 0.84-1.13), but predict that λ will decline under continued climate warming, resulting in a 62% chance of extinction by the 2080s because of compounding negative effects on early and late life history stages. By the 2080s, our models predict that larval mortality will increase by 17% as a result of increased pond drying, and adult survival will decrease by 7% as winter length and summer precipitation continue to decrease. We find that reduced larval survival drives initial declines in the 2040s, but further declines in the 2080s are compounded by decreases in adult survival. Our results demonstrate the need to understand the potential for compounding or compensatory effects within different life history stages to exacerbate or buffer the effects of climate change on population growth rates through time.
人为气候变化给个体在其整个生命周期中的生长、繁殖和生存带来了挑战和机遇。生命史各阶段的人口补偿有可能缓冲种群数量的下降，但相反，累积的负面影响可能导致种群加速下降和灭绝。在美国太平洋西北地区的山地生态系统中，气温升高导致降雪主导的降水事件向降雨主导的降水事件转变，减少了积雪量。对于两栖动物等变温动物来说，温暖的冬季可以减少临界最低温度的出现频率，并延长夏季生长季节，有利于变态后的阶段，但也可能增加冬季的代谢成本，从而降低存活率。较低的积雪量也会导致湿地在夏季更早或更频繁地干涸，增加幼虫干枯的风险。为了评估这些挑战和机遇在物种生命史中是如何相互作用的，我们收集了华盛顿州奥林匹克国家公园的喀斯喀特蛙（Rana cascadae）的人口统计数据，以便在当前和未来（A1B、2040 年代和 2080 年代）环境条件下对基于阶段的随机矩阵种群模型进行参数化。我们使用特定流域的水文模型估计每年因干涸而损失的繁殖努力的比例，并将其与一项将 15 年的 R. cascadae 丰度数据与一系列气候变量相关联的分析结合起来。我们估计当前的种群增长率（λ）为 0.97（95%置信区间 0.84-1.13），但预测随着气候持续变暖，λ 将下降，到 2080 年代，由于对早期和晚期生命史阶段的累积负面影响，灭绝的可能性将达到 62%。到 2080 年代，我们的模型预测，由于池塘干涸增加，幼虫死亡率将增加 17%，而随着冬季长度和夏季降水继续减少，成年存活率将下降 7%。我们发现，幼虫存活率的降低导致 2040 年代初期种群数量的下降，但 2080 年代进一步的下降是由于成年存活率的下降而加剧的。我们的研究结果表明，需要了解不同生命史阶段的累积或补偿效应的潜力，以随着时间的推移加剧或缓冲气候变化对种群增长率的影响。
