Ecol Appl. 2014 Jun;24(4):895-912. doi: 10.1890/13-0753.1.
Predicting how climate change is likely to interact with myriad other stressors that threaten species of conservation concern is an essential challenge in aquatic ecosystems. This study provides a framework to accomplish this task in salmon-bearing streams of the northwestern United States, where land-use-related reductions in riparian shading have caused changes in stream thermal regimes, and additional warming from projected climate change may result in significant losses of coldwater fish habitat over the next century. Predatory, nonnative smallmouth bass have also been introduced into many northwestern streams, and their range is likely to expand as streams warm, presenting an additional challenge to the persistence of threatened Pacific salmon. The goal of this work was to forecast the interactive effects of climate change, riparian management, and nonnative species on stream-rearing salmon and to evaluate the capacity of restoration to mitigate these effects. We intersected downscaled global climate forecasts with a local-scale water temperature model to predict mid- and end-of-century temperatures in streams in the Columbia River basin. We compared one stream that is thermally impaired due to the loss of riparian vegetation and another that is cooler and has a largely intact riparian corridor. Using the forecasted stream temperatures in conjunction with fish-habitat models, we predicted how stream-rearing chinook salmon and bass distributions would change as each stream warmed. In the highly modified stream, end-of-century warming may cause near total loss of chinook salmon-rearing habitat and a complete invasion of the upper watershed by bass. In the less modified stream, bass were thermally restricted from the upstream-most areas. In both systems, temperature increases resulted in higher predicted spatial overlap between stream-rearing chinook salmon and potentially predatory bass in the early summer (two- to fourfold increase) and greater abundance of bass. We found that riparian restoration could prevent the extirpation of chinook salmon from the more altered stream and could also restrict bass from occupying the upper 31 km of salmon-rearing habitat. The proposed methodology and model predictions are critical for prioritizing climate-change adaptation strategies before salmonids are exposed to both warmer water and greater predation risk by nonnative species.
预测气候变化可能如何与威胁保护物种的众多其他压力因素相互作用，是水生生态系统面临的一项重要挑战。本研究为实现这一目标提供了一个框架，该目标针对的是美国西北部有鲑鱼栖息的溪流，在这些溪流中，与土地利用有关的河岸植被减少导致了溪流热状况的变化，而预计气候变化引起的额外升温可能导致在未来一个世纪冷水鱼类栖息地的大量丧失。具有掠夺性的非本地小口黑鲈也已被引入到许多美国西北部溪流中，随着溪流变暖，其分布范围可能会扩大，这对受威胁的太平洋鲑鱼的生存构成了另一个挑战。这项工作的目标是预测气候变化、河岸管理和外来物种对溪流育肥鲑鱼的相互影响，并评估恢复的能力来减轻这些影响。我们将经过降尺度的全球气候预测与局部尺度的水温模型相交，以预测哥伦比亚河流域溪流的中期和本世纪末的温度。我们比较了一条因河岸植被丧失而受热影响的溪流和另一条较冷且拥有大部分完整河岸带的溪流。利用预测的溪流温度，结合鱼类栖息地模型，我们预测了随着每条溪流升温，溪流育肥的奇努克鲑鱼和鲈鱼的分布将如何变化。在高度受干扰的溪流中，本世纪末的变暖可能导致奇努克鲑鱼育肥栖息地几乎完全丧失，鲈鱼完全入侵上游流域。在受干扰较小的溪流中，鲈鱼的温度限制使其无法到达最上游的区域。在这两个系统中，温度升高导致夏季早期溪流育肥的奇努克鲑鱼和潜在的掠夺性鲈鱼之间的空间重叠预测更高（增加两到四倍），以及鲈鱼的数量更多。我们发现，河岸恢复可以防止奇努克鲑鱼从受干扰较大的溪流中灭绝，也可以限制鲈鱼占据鲑鱼育肥栖息地的上游 31 公里。拟议的方法和模型预测对于在鲑鱼暴露于更高水温和更大的外来物种捕食风险之前，优先制定适应气候变化的策略至关重要。
