Trophic cascades are important features of aquatic ecosystems, but much variation in their strength remains unexplained. Disturbance could restrict cascade occurrence by limiting predator distribution, and increase cascade strength by lowering defended herbivore abundance. These possibilities were investigated in 20 New Zealand rivers varying both in flooding disturbance (measured by bed movement) and presence of non-native predatory trout. Trout were often, but not always, associated with indirectly increasing algal abundance compared to similar rivers with native galaxiid fishes. Floods explained variation in cascades by (1) resetting algal abundance such that algal minima were related to bed movement; (2) preventing occurrence by restricting trout abundance in the most disturbed rivers; and (3) increasing potential cascade strength by removing defended herbivores. These observations indicate strong nonlinear influences of disturbance on both trophic cascade occurrence and maximum strength which will be important to consider as climate change alters disturbance regimes.

中文翻译：

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洪水干扰调节由鳟鱼引起的溪流营养级联的强度

营养级联是水生生态系统的重要特征，但其强度的许多变化仍然无法解释。干扰可以通过限制捕食者分布来限制级联的发生，并通过降低受保护的食草动物丰度来增加级联强度。这些可能性在 20 条新西兰河流中进行了调查，这些河流的洪水干扰（通过河床运动测量）和非本地捕食性鳟鱼的存在都有所不同。与具有原生 galaxiid 鱼类的类似河流相比，鳟鱼通常（但并非总是）与间接增加的藻类丰度有关。洪水通过（1）重置藻类丰度来解释级联变化，使藻类最小值与床运动有关；(2) 通过限制受干扰最严重的河流中的鳟鱼数量来防止发生；(3) 通过移除防御的食草动物来增加潜在的级联强度。这些观察结果表明，扰动对营养级联发生和最大强度都有强烈的非线性影响，随着气候变化改变扰动机制，这将是重要的考虑因素。