River regulation can modify natural flow regimes with deleterious effects on aquatic communities. While the effects of flow manipulation on the physical environment and populations and assemblages of aquatic organisms have been described thoroughly, how and to what extent river regulation influences ecosystem processes like food web architecture is less studied. Emergent aquatic insect prey can provide an important food resource to riparian consumers like birds and bats with concomitant consequences for nutrient cycling through aquatic–terrestrial food webs, thus potentially increasing the spatial influence of river regulation into the riparian zone and beyond. We used naturally abundant stable isotopes of carbon and nitrogen to compare food web architecture (trophic position and reliance on an aquatic nutritional pathway) leading to birds and bats between a regulated river, the Tuolumne River downstream of Hetch Hetchy Reservoir, and an adjacent unregulated river, the Merced River, located in Yosemite National Park on the west slope of the Sierra Nevada, California, USA. We found that both birds and bats derived >50% of their nutrition from food webs originating in photosynthesis by algae. In addition, birds and bats occupied a similar trophic position to predatory fish in other systems. Both birds and bats seemed to rely more strongly on an aquatic nutritional pathway during the dryer year of our study period, underscoring the potential importance of emergent aquatic prey as a water subsidy in dry systems and in dry years. In the Tuolumne River, reservoir managers strive to simulate characteristics of the natural flow regime, including seasonal scouring flows and prolonged floodplain inundation. Although we found no conclusive evidence of an effect of river regulation on food web responses, our study suggests that nutrient cycling through aquatic–terrestrial food webs expands the potential influence of river regulation to organisms and ecosystems typically characterized as terrestrial.

中文翻译：

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河流食物链导致两条中阶河流中的河岸蝙蝠和鸟类

河流调节会改变自然流向，对水生生物造成有害影响。尽管已经充分描述了流量操纵对自然环境，水生生物种群和集合的影响，但对河流调节如何影响食物网架构等生态系统过程的方式和程度的研究却很少。新兴的水生昆虫猎物可为鸟类和蝙蝠等河岸消费者提供重要的食物资源，并伴随着通过水陆食物网的养分循环，从而潜在地增加了对河岸地区及其他地区的河流管制的空间影响。我们使用了自然丰富的碳和氮的稳定同位素来比较食物网的结构（营养位置和对水生营养途径的依赖），从而导致受管制的河流，Hetch Hetchy水库下游的Tuolumne河与相邻的不受管制的河流之间形成鸟类和蝙蝠，默塞德河（Merced River），位于美国加利福尼亚内华达山脉西坡的优胜美地国家公园。我们发现鸟类和蝙蝠都从藻类进行光合作用的食物网中获取了超过50％的营养。此外，在其他系统中，鸟类和蝙蝠的营养位置与掠食性鱼类相似。在研究期的干燥年份，鸟类和蝙蝠似乎都更加依赖水生营养途径，强调了在干旱系统和干旱年份，新兴水生猎物作为水补贴的潜在重要性。在Tuolumne河中，水库管理人员致力于模拟自然流量状态的特征，包括季节性的冲刷流量和漫长的洪泛区淹没。尽管我们没有发现关于河流调节对食物网响应的影响的确凿证据，但我们的研究表明，通过水生-陆地食物网的养分循环将河流调节对典型地为陆地的生物和生态系统的潜在影响扩大了。