Top-down cascade effects are among the most important mechanisms underlying community structure and abundance dynamics in aquatic and terrestrial ecosystems worldwide. A current challenge is understanding the factors controlling trophic cascade strength under global environmental changes. Here, we synthesized 161 global sites to analyze how multiple factors influence consumer-resource interactions with fish in freshwater ecosystems. Fish have a profound negative effect on zooplankton and water clarity but positive effects on primary producers and water nutrients. Furthermore, fish trophic levels can modify the strength of trophic cascades, but an even number of food chain length does not have a negative effect on primary producers in real ecosystems. Eutrophication, warming, and predator abundance strengthen the trophic cascade effects on phytoplankton, suggesting that top-down control will be increasingly important under future global environmental changes. We found no influence or even an increasing trophic cascade strength (e.g., phytoplankton) with increasing latitude, which does not support the widespread view that the trophic cascade strength increases closer to the equator. With increasing temporal and spatial scales, the experimental duration has an accumulative effect, whereas the experimental size is not associated with the trophic cascade strength. Taken together, eutrophication, warming, temporal scale, and predator trophic level and abundance are pivotal to understanding the impacts of multiple environmental factors on the trophic cascade strength. Future studies should stress the possible synergistic effect of multiple factors on the food web structure and dynamics.

中文翻译：

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淡水生态系统中营养级联强度的决定因素：全球分析

自上而下的级联效应是全球水生和陆地生态系统群落结构和丰度动态的最重要机制之一。当前的挑战是了解在全球环境变化下控制营养级联强度的因素。在这里，我们综合了 161 个全球站点，以分析多种因素如何影响淡水生态系统中消费者与资源的相互作用。鱼类对浮游动物和水的透明度有深远的负面影响，但对初级生产者和水的养分有积极的影响。此外，鱼类的营养水平可以改变营养级联的强度，但偶数的食物链长度不会对真实生态系统中的初级生产者产生负面影响。富营养化、变暖、和捕食者丰度加强了对浮游植物的营养级联效应，表明在未来的全球环境变化下自上而下的控制将变得越来越重要。我们发现随着纬度的增加没有影响甚至增加营养级联强度（例如浮游植物），这不支持营养级联强度在接近赤道时增加的普遍观点。随着时间和空间尺度的增加，实验持续时间具有累积效应，而实验规模与营养级联强度无关。总之，富营养化、变暖、时间尺度以及捕食者的营养水平和丰度对于理解多种环境因素对营养级联强度的影响至关重要。