Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, V6T 1Z4 Canada.
Ecology. 2013 May;94(5):1123-30. doi: 10.1890/12-0428.1.
Understanding how entire ecosystems maintain stability in the face of climatic and human disturbance is one of the most fundamental challenges in ecology. Theory suggests that a crucial factor determining the degree of ecosystem stability is simply the degree of synchrony with which different species in ecological food webs respond to environmental stochasticity. Ecosystems in which all food-web pathways are affected similarly by external disturbance should amplify variability in top carnivore abundance over time due to population interactions, whereas ecosystems in which a large fraction of pathways are nonresponsive or even inversely responsive to external disturbance will have more constant levels of abundance at upper trophic levels. To test the mechanism underlying this hypothesis, we used over half a century of demographic data for multiple species in the Serengeti (Tanzania) ecosystem to measure the degree of synchrony to variation imposed by an external environmental driver, the El Niño Southern Oscillation (ENSO). ENSO effects were mediated largely via changes in dry-season vs. wet-season rainfall and consequent changes in vegetation availability, propagating via bottom-up effects to higher levels of the Serengeti food web to influence herbivores, predators and parasites. Some species in the Serengeti food web responded to the influence of ENSO in opposite ways, whereas other species were insensitive to variation in ENSO. Although far from conclusive, our results suggest that a diffuse mixture of herbivore responses could help buffer top carnivores, such as Serengeti lions, from variability in climate. Future global climate changes that favor some pathways over others, however, could alter the effectiveness of such processes in the future.
理解整个生态系统如何在面对气候和人为干扰时保持稳定，是生态学中最基本的挑战之一。理论表明，决定生态系统稳定性程度的一个关键因素，仅仅是生态食物网中不同物种对环境随机性的同步程度。如果所有的食物网途径都受到外部干扰的相似影响，那么由于种群相互作用，顶级捕食者的丰度在时间上应该会增加变异性，而在那些大部分途径对外部干扰没有反应甚至相反的生态系统中，上营养级的丰度水平应该更稳定。为了检验这一假设的机制，我们利用半个多世纪以来在坦桑尼亚塞伦盖蒂生态系统中对多个物种的人口统计数据，来衡量对外部环境驱动因素——厄尔尼诺南方涛动（ENSO）的变化的同步程度。ENSO 的影响主要通过旱季与雨季降雨量的变化以及由此产生的植被可利用性的变化来介导，通过自下而上的影响传播到塞伦盖蒂食物网的更高层次，从而影响食草动物、捕食者和寄生虫。塞伦盖蒂食物网中的一些物种对 ENSO 的影响以相反的方式作出反应，而其他物种则对 ENSO 的变化不敏感。尽管还远不能得出结论，但我们的结果表明，食草动物反应的分散混合可能有助于缓冲顶级捕食者，如塞伦盖蒂狮子，免受气候变异性的影响。然而，未来有利于某些途径而不利于其他途径的全球气候变化，可能会改变这些过程在未来的有效性。
