Amundrud Sarah L, Srivastava Diane S
Ecology. 2016 Jun;97(6):1475-83. doi: 10.1890/15-1638.1.
Species interactions can be important mediators of community and ecosystem responses to environmental stressors. However, we still lack a mechanistic understanding of the indirect ecological effects of stress that arise via altered species interactions. To understand how species interactions will be altered by environmental stressors, we need to know if the species that are vulnerable to such stressors also have large impacts on the ecosystem. As predators often exhibit certain traits that are linked to a high vulnerability to stress (e.g., large body size, long generation time), as well as having large effects on communities (e.g., top-down trophic effects), predators may be particularly likely to mediate ecological effects of environmental stress. Other functional groups, like facilitators, are known to have large impacts on communities, but their vulnerability to perturbations remains undocumented. Here, we use aquatic insect communities in bromeliads to examine the indirect effects of an important stressor (drought) on community and ecosystem responses. In a microcosm experiment, we manipulated predatory and facilitative taxa under a range of experimental droughts, and quantified effects on community structure and ecosystem function. Drought, by adversely affecting the top predator, had indirect cascading effects on the entire food web, altering community composition and decomposition. We identified the likely pathway of how drought cascaded through the food web from the top-down as drought -->predator --> shredder --> decomposition. This stress-induced cascade depended on predators exhibiting both a strong vulnerability to drought and large impacts on prey (especially shredders), as well as shredders exhibiting high functional importance as decomposers.
物种间相互作用可能是群落和生态系统对环境压力源做出响应的重要调节因素。然而，我们仍然缺乏对因物种相互作用改变而产生的压力间接生态效应的机制理解。为了了解环境压力源将如何改变物种间相互作用，我们需要知道那些易受此类压力源影响的物种是否也对生态系统有重大影响。由于捕食者通常表现出某些与高压力易感性相关的特征（例如，体型大、世代时间长），同时对群落有重大影响（例如，自上而下的营养效应），捕食者可能特别容易介导环境压力的生态效应。其他功能类群，如促进者，已知对群落有重大影响，但其对干扰的易感性仍未得到记录。在这里，我们利用凤梨科植物中的水生昆虫群落来研究一种重要压力源（干旱）对群落和生态系统响应产生的间接影响。在一个微观实验中，我们在一系列实验干旱条件下操纵捕食性和促进性类群，并量化其对群落结构和生态系统功能的影响。干旱通过对顶级捕食者产生不利影响，对整个食物网产生间接级联效应，改变群落组成和分解过程。我们确定了干旱自上而下通过食物网级联的可能途径为干旱→捕食者→碎食者→分解。这种由压力引发的级联效应取决于捕食者表现出对干旱的高度易感性和对猎物（尤其是碎食者）的重大影响，以及碎食者作为分解者表现出的高功能重要性。
