Disturbance-mediated consumer assemblages determine fish community structure and moderate top-down influences through bottom-up constraints,Journal of Animal Ecology

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Disturbance-mediated consumer assemblages determine fish community structure and moderate top-down influences through bottom-up constraints
Journal of Animal Ecology ( IF 3.5 ) Pub Date : 2020-01-28 , DOI: 10.1111/1365-2656.13168
Phillip G Jellyman _{1,

2} , Angus R McIntosh ₁

Affiliation

Disturbance is a strong structuring force that can influence the strength of species interactions at all trophic levels, but controls on the contributions to community structure of top-down and bottom-up processes across such gradients remain poorly understood. Changes in the composition of predator and consumer assemblages, and their associated traits, across gradients of environmental harshness (e.g., flooding) are likely to be a particularly important influence on the strength of top-down control and may drive bottom-up constraints. We examined how consumers with particular traits, and the predators that consumed them, varied across a gradient of stream flooding disturbance and used experiments to assess the predation impact on those contrasting consumer communities (ultimately quantifying how flood disturbance altered the strength of top-down control). Consumer community composition and mobility were strongly related to flood disturbance; the biomass and drift of protected primary consumers (i.e., those with morphological defences) decreased with increasing flood disturbance. Predatory fish species had different disturbance niches, and path analysis identified that both direct flood-disturbance effects and indirect bottom-up constraints of flood-disturbance on consumers influenced predatory fish composition and biomass. Fishes generally fed most effectively on consumer types associated with their particular niche, but all fishes were strongly size-selective when feeding on protected consumers. Although protected consumers did not grow large enough to escape predation, an in situ experiment showed protected consumers were at a reduced risk of predation as disturbance increased compared to unprotected consumers. Overall, top-down control declined with flood disturbance, but the effect depended on consumer traits. Predatory fishes were only capable of exerting top-down control on protected consumers in benign habitats but impacted unprotected consumers across a larger range of the disturbance gradient. Collectively our findings suggest that a shift towards a more disturbed state will probably result in reduced predator impacts and a weakening of top-down control. Moreover, predicted increases in the frequency and intensity of climatic events causing disturbance, such as flooding, are likely to result in a community shift that disproportionately impacts protected consumers and the predators that utilise them as prey through the subsequent bottom-up constraints.

中文翻译：

干扰介导的消费者组合决定了鱼类群落结构，并通过自下而上的约束来调节自上而下的影响

扰动是一种强大的结构力，可以影响所有营养级别的物种相互作用的强度，但对跨这种梯度的自上而下和自下而上过程对群落结构的贡献的控制仍然知之甚少。掠食者和消费者组合的组成及其相关特征的变化，跨越环境恶劣程度（例如，洪水）的梯度，可能对自上而下的控制强度产生特别重要的影响，并可能导致自下而上的约束。我们研究了具有特定特征的消费者以及消耗它们的掠食者，不同的河流洪水干扰梯度变化，并使用实验来评估捕食对那些对比鲜明的消费者社区的影响（最终量化洪水干扰如何改变自上而下的控制强度）。消费者社区的组成和流动性与洪水干扰密切相关；受保护的初级消费者（即具有形态防御的消费者）的生物量和漂移随着洪水干扰的增加而减少。掠食性鱼类具有不同的干扰生态位，路径分析确定洪水干扰对消费者的直接影响和间接自下而上的约束影响了掠食性鱼类的组成和生物量。鱼类通常以与其特定利基相关的消费者类型为食，但所有鱼类在以受保护的消费者为食时都具有很强的尺寸选择性。尽管受保护的消费者没有长到足以逃脱捕食，但原位实验表明，与未受保护的消费者相比，受保护的消费者因干扰增加而遭受捕食的风险降低。总体而言，自上而下的控制随着洪水干扰而下降，但效果取决于消费者的特征。掠食性鱼类只能在良性栖息地对受保护的消费者施加自上而下的控制，但会在更大范围的干扰梯度上影响未受保护的消费者。总的来说，我们的研究结果表明，转向更受干扰的状态可能会减少捕食者的影响并削弱自上而下的控制。而且，

更新日期：2020-01-28

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