Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523-1499, USA.
Proc Biol Sci. 2013 Feb 6;280(1756):20122977. doi: 10.1098/rspb.2012.2977. Print 2013 Apr 7.
Efforts to restore ecosystems often focus on reintroducing apex predators to re-establish coevolved relationships among predators, herbivores and plants. The preponderance of evidence for indirect effects of predators on terrestrial plant communities comes from ecosystems where predators have been removed. Far less is known about the consequences of their restoration. The effects of removal and restoration are unlikely to be symmetrical because removing predators can create feedbacks that reinforce the effects of predator loss. Observational studies have suggested that the reintroduction of wolves to Yellowstone National Park initiated dramatic restoration of riparian ecosystems by releasing willows from excessive browsing by elk. Here, we present results from a decade-long experiment in Yellowstone showing that moderating browsing alone was not sufficient to restore riparian zones along small streams. Instead, restoration of willow communities depended on removing browsing and restoring hydrological conditions that prevailed before the removal of wolves. The 70-year absence of predators from the ecosystem changed the disturbance regime in a way that was not reversed by predator reintroduction. We conclude that predator restoration may not quickly repair effects of predator removal in ecosystems.
人们常常致力于恢复生态系统，重新引入顶级捕食者，以重新建立捕食者、食草动物和植物之间共同进化的关系。大量证据表明，捕食者对陆地植物群落的间接影响来自于已去除捕食者的生态系统。而关于它们恢复的后果，我们知之甚少。移除和恢复的效果不太可能是对称的，因为移除捕食者会产生反馈，从而强化捕食者损失的影响。观察性研究表明，黄石国家公园狼群的重新引入通过释放柳树免受麋鹿过度啃食，引发了河岸生态系统的显著恢复。在这里，我们展示了黄石公园长达十年的实验结果，表明仅调节啃食本身不足以恢复小溪沿岸的河岸带。相反，柳树群落的恢复取决于去除啃食行为，并恢复在狼群移除之前占主导地位的水文学条件。七十年来，该生态系统中缺乏捕食者，以一种不能通过捕食者再引入来逆转的方式改变了干扰机制。我们的结论是，捕食者的恢复可能不会迅速修复捕食者移除对生态系统的影响。
