Department of Biology and Tyson Research Center, Washington University in Saint Louis, Saint Louis, Missouri 63130, USA.
Ecology. 2010 Mar;91(3):637-43. doi: 10.1890/09-0262.1.
Habitat isolation is well known to alter patterns of species' abundance, richness, and the ratios of predators : prey. Less clear, however, is how isolation alters interactions within food webs. Here, we present the results from an experiment performed in artificial ponds (mesocosms) manipulating habitat isolation crossed with a predator reduction treatment to disentangle how isolation mediates the top-down effect of predators. The strength of the trophic cascade, from predators, through herbivores, to producers, was considerably stronger in connected than in isolated habitats. We further found that the overall richness of both predator and herbivore species declined strongly with isolation. Experimental predator reductions suggest that the mechanism underlying the herbivore response was likely mediated by a keystone predator effect; when predators were reduced, herbivore richness was lower, and there was no discernable effect of isolation on herbivore richness. Finally, we found that the composition of predators in more isolated habitats consisted of species that were smaller and likely less effective predators than species that persisted in less isolated habitats. In all, our experiment showed that habitat isolation can alter the structure of communities by a combination of direct effects of the species in question, as well as effects mediated through their interactions in the food web.
生境隔离众所周知会改变物种丰度、丰富度和捕食者与猎物比例的模式。然而，生境隔离如何改变食物网内的相互作用还不太清楚。在这里，我们介绍了在人工池塘（中观模型）中进行的一项实验的结果，该实验通过操纵生境隔离和捕食者减少处理来分离隔离如何介导捕食者的自上而下的影响。与隔离生境相比，在连通生境中，从捕食者到食草动物再到生产者的营养级联强度要强得多。我们还发现，捕食者和食草动物的整体丰富度都随着隔离而强烈下降。实验性捕食者减少表明，食草动物反应的机制可能是通过关键捕食者效应介导的；当捕食者减少时，食草动物的丰富度较低，而隔离对食草动物的丰富度没有明显的影响。最后，我们发现，在隔离程度较高的生境中，捕食者的组成由体型较小、可能捕食效果较差的物种组成，而在隔离程度较低的生境中则有体型较大、捕食效果较好的物种存在。总之，我们的实验表明，生境隔离可以通过受关注物种的直接影响以及通过它们在食物网中的相互作用的中介影响来改变群落的结构。
