Many anthropogenic stressors broadly inflict mortality or reduce fecundity, including habitat destruction, pollution, climate change, invasive species, and multispecies harvesting. Here, we show—in four analytical models of interspecies competition—that broadly inflicted stressors disproportionately cause competitive exclusions within groups of ecologically similar species. As a result, we predict that ecosystems become progressively thinner—that is, they have progressively less functional redundancy—as broadly inflicted stressors become progressively more intense. This may negatively affect the temporal stability of ecosystem functions, but it also buffers ecosystem productivity against stress by favoring species less sensitive to the stressors. Our main result follows from the weak limiting similarity principle: species with more similar ecological niches compete more strongly, and their coexistence can be upset by smaller perturbations. We show that stressors can cause indirect competitive exclusions at much lower stressor intensity than needed to directly cause species extinction, consistent with the finding of empirical studies that species interactions are often the proximal drivers of local extinctions. The excluded species are more sensitive to the stressor relative to their ecologically similar competitors. Moreover, broadly inflicted stressors may cause hydra effects—where higher stressor intensity results in higher abundance for a species with lower sensitivity to the stressor than its competitors. Correlations between stressor impacts and ecological niches reduce the potential for indirect competitive exclusions, but they consequently also reduce the buffering effect of ecosystem thinning on ecosystem productivity. Our findings suggest that ecosystems experiencing stress may continue to provision ecosystem services but lose functional redundancy and stability.

中文翻译：

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广泛施加的压力会导致生态系统变薄。


许多人为压力源广泛造成死亡或降低繁殖力，包括栖息地破坏、污染、气候变化、入侵物种和多物种收获。在这里，我们在四种种间竞争的分析模型中表明，广泛施加的压力源不成比例地导致生态相似物种群体内的竞争排斥。因此，我们预测，随着广泛施加的压力源变得越来越强烈，生态系统将变得越来越薄，也就是说，它们的功能冗余越来越少。这可能会对生态系统功能的时间稳定性产生负面影响，但它也通过有利于对压力源不太敏感的物种来缓冲生态系统的生产力以应对压力。我们的主要结果遵循弱限制相似性原则：生态位越相似的物种竞争越激烈，它们的共存可能会被较小的扰动所扰乱。我们表明，压力源可以在比直接导致物种灭绝所需的压力源强度低得多的情况下引起间接竞争排斥，这与实证研究的发现一致，即物种相互作用往往是局部灭绝的直接驱动因素。相对于生态相似的竞争者，被排除的物种对压力源更敏感。此外，广泛施加的压力可能会导致水螅效应——较高的压力强度会导致对压力的敏感性低于竞争对手的物种的丰度更高。压力源影响和生态位之间的相关性降低了间接竞争排斥的可能性，但它们也因此降低了生态系统稀疏对生态系统生产力的缓冲作用。 我们的研究结果表明，经历压力的生态系统可能会继续提供生态系统服务，但会失去功能冗余和稳定性。