1. Most of the world's large rivers are dammed for the purposes of water storage, flood control, and power production. Damming rivers fundamentally alters water temperature and flows in tailwater ecosystems, which in turn affects the presence and abundance of downstream biota.
2. We collaborated with more than 200 citizen scientists to collect 2,194 light trap samples across 2 years and more than 2,000 river km. Samples contained 16,222 net‐spinning caddisfly (Hydropsyche) individuals across six species. We used these data to model the distribution of Hydropsyche throughout the Colorado River Basin in the western U.S.A. to identify the roles of water temperature, flows, and species‐specific morphology in determining aquatic species distributions throughout a large arid watershed that has been heavily altered by damming.
3. We predicted that water temperatures would determine Hydropsyche presence and abundance to a greater extent than diel variation in river stage associated with hydropower production. Among many species, adult female Hydropsychids are morphologically adapted to swim to deep‐water oviposition sites. We predicted that the presence of this ability would negate the otherwise deleterious effects of high stage change on caddisfly egg mortality.
4. We found that distributions of the two most widespread species, Hydropsyche occidentalis and Hydropsyche oslari (92% of total Hydropsyche captured), were both predicted by water temperatures. However, we also found that the abundance of H. oslari decreased by as much as 10‐fold as diel stage change increased, despite the presence of female morphological adaptations for deep‐water oviposition. We found sexual dimorphism and evidence for deep‐water swimming adaptations in 5/6 species.
5. Our results show that net‐spinning caddisflies have species‐specific responses to environmental variation and suggest that environmental flows designed to reduce diel stage change and destabilise water temperatures may improve habitat quality for these ubiquitous and important aquatic insects.

中文翻译：

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大型调节河流中的网纺线虫分布

1. 世界上大多数大河都是为了蓄水，防洪和发电而筑坝的。筑坝河流从根本上改变了水温和尾水生态系统的流量，进而影响了下游生物群的存在和丰度。
2. 我们与200多位公民科学家合作，在2年内和2,000多公里的河流中收集了2,194个光阱样品。样本包含六个物种中的16,222个净纺丝虫（Hydropsyche）。我们使用这些数据来模拟美国西部科罗拉多河盆地内Hydropsyche的分布，以确定水温，流量和物种特定形态在确定一个大型干旱流域中水生物种分布方面的作用，该流域已被严重改变大坝。
3. 我们预测，与水力发电相关的河流水位的狄尔变化相比，水温将在更大程度上决定Hydropsyche的存在和丰度。在许多物种中，成年雌性水psych虫在形态上适合游泳到深水产卵位。我们预测，此功能的存在将消除高阶变化对蝇卵死亡率的其他有害影响。
4. 我们发现这两个最普遍的物种是分布Hydropsyche 望江南和Hydropsyche oslari（占92％Hydropsyche捕获），都是由水温预测。但是，我们也发现，尽管女性对深水产卵的形态适应存在，但随着diel阶段变化的增加，H。oslari的丰度下降了多达10倍。我们发现性二态性和5/6种深水游泳适应性的证据。
5. 我们的结果表明，纺网的虫对环境变化具有物种特定的响应，并表明旨在减少diel阶段变化和使水温不稳定的环境流量可能会改善这些普遍存在的重要水生昆虫的栖息地质量。