Natural and anthropogenic pressures exert influence on ecosystem structure and function by affecting the physiology and behavior of organisms, as well as the trophic interactions within assemblages. Therefore, understanding how multiple stressors affect aquatic ecosystems can improve our ability to manage and protect these ecosystems and contribute to understanding fundamental ecological principles. Here, we conducted a mesocosm experiment to ascertain the individual and combined effects of multiple stressors on trophic interactions within species in freshwater ecosystems. Furthermore, we investigated how species respond to such changes by adapting their food resources. To mimic a realistic food web, we selected fish and shrimp as top predators, gastropods, zooplankton and zoobenthos as intermediate consumers, with producers (macrophytes, periphyton and phytoplankton) and detritus as basal resources. Twelve different treatments included a control, nutrient loading only, herbicide exposure only, and a combination of nutrient loading and herbicide exposure, each replicated under ambient temperature, constant warming and multiple heat waves to simulate environmental stressors. Our results demonstrated that antagonistic interactions between environmental stressors were widespread in trophic interactions, with a more pronounced and less intense impact observed for the high trophic level species. The responses of freshwater communities to environmental stressors are complex, involving direct effects on individual species as well as indirect effects through species interactions. Moreover, our results confirmed that the combinations of stressors, but not individual stressors, led to a shift to herbivory in top predators, indicating that multiple stressors can be more detrimental to organisms than individual stressors alone. These findings elucidate how changes in the resource utilization of species induced by environmental stressors can potentially influence species interactions and the structural dynamics of food webs in freshwater ecosystems.

中文翻译：

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多种压力源对淡水食物网的影响：来自中生态系统实验的证据

自然和人为压力通过影响生物体的生理和行为以及组合内的营养相互作用来影响生态系统的结构和功能。因此，了解多种压力因素如何影响水生生态系统可以提高我们管理和保护这些生态系统的能力，并有助于理解基本的生态原理。在这里，我们进行了一项中生态实验，以确定多种压力源对淡水生态系统物种内营养相互作用的单独和组合影响。此外，我们还研究了物种如何通过调整食物资源来应对这些变化。为了模拟真实的食物网，我们选择鱼和虾作为顶级捕食者，腹足动物、浮游动物和底栖动物作为中间消费者，生产者（大型植物、附生植物和浮游植物）和碎屑作为基础资源。十二种不同的处理包括对照、仅养分负载、仅除草剂暴露、以及养分负载和除草剂暴露的组合，每种处理在环境温度、持续变暖和多次热浪下重复以模拟环境压力源。我们的结果表明，环境压力源之间的拮抗相互作用在营养级相互作用中广泛存在，对于高营养级物种观察到的影响更明显且不太强烈。淡水群落对环境压力的反应是复杂的，涉及对单个物种的直接影响以及通过物种相互作用产生的间接影响。此外，我们的结果证实，压力源的组合，而不是单个压力源，导致顶级捕食者转向草食性，这表明多个压力源对生物体的危害可能比单独的压力源更大。这些发现阐明了环境压力引起的物种资源利用的变化如何可能影响淡水生态系统中物种相互作用和食物网的结构动态。