Burgess Matthew G, Fredston-Hermann Alexa, Tilman David, Loreau Michel, Gaines Steven D
Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, 216 UCB, Boulder, CO 80309, USA.
Environmental Studies Program, University of Colorado, Boulder, CO 80303, USA.
Theor Ecol. 2019 Jun;12(2):207-223. doi: 10.1007/s12080-019-0417-4. Epub 2019 Feb 26.
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 -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.
许多人为压力源广泛地造成死亡或降低繁殖力，包括栖息地破坏、污染、气候变化、入侵物种和多物种捕捞。在此，我们在四个种间竞争分析模型中表明，广泛造成的压力源会不成比例地在生态相似的物种群体中导致竞争排斥。因此，我们预测，随着广泛造成的压力源强度不断增加，生态系统会逐渐地——也就是说，其功能冗余会逐渐减少。这可能会对生态系统功能的时间稳定性产生负面影响，但它也通过青睐对压力源不太敏感的物种来缓冲生态系统生产力免受压力影响。我们的主要结果源于弱极限相似性原则：生态位更相似的物种竞争更激烈，较小的干扰就可能打破它们的共存。我们表明，压力源导致间接竞争排斥所需的强度远低于直接导致物种灭绝所需的强度，这与实证研究的结果一致，即物种相互作用往往是局部灭绝的直接驱动因素。相对于其生态相似的竞争者，被排斥的物种对压力源更敏感。此外，广泛造成的压力源可能会导致九头蛇效应——压力源强度越高，对于一个对压力源敏感度低于其竞争者的物种来说，其丰度就越高。压力源影响与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简化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。
