Peacor S D, Werner E E
Department of Biology, University of Michigan, Ann Arbor, MI 48109, USA.
Proc Natl Acad Sci U S A. 2001 Mar 27;98(7):3904-8. doi: 10.1073/pnas.071061998. Epub 2001 Mar 20.
Many prey modify traits in response to predation risk and this modification of traits can influence the prey's resource acquisition rate. A predator thus can have a "nonlethal" impact on prey that can lead to indirect effects on other community members. Such indirect interactions are termed trait-mediated indirect interactions because they arise from a predator's influence on prey traits, rather than prey density. Because such nonlethal predator effects are immediate, can influence the entire prey population, and can occur over the entire prey lifetime, we argue that nonlethal predator effects are likely to contribute strongly to the net indirect effects of predators (i.e., nonlethal effects may be comparable in magnitude to those resulting from killing prey). This prediction was supported by an experiment in which the indirect effects of a larval dragonfly (Anax sp.) predator on large bullfrog tadpoles (Rana catesbeiana), through nonlethal effects on competing small bullfrog tadpoles, were large relative to indirect effects caused by density reduction of the small tadpoles (the lethal effect). Treatments in which lethal and nonlethal effects of Anax were manipulated independently indicated that this result was robust for a large range of different combinations of lethal and nonlethal effects. Because many, if not most, prey modify traits in response to predators, our results suggest that the magnitude of interaction coefficients between two species may often be dynamically related to changes in other community members, and that many indirect effects previously attributed to the lethal effects of predators may instead be due to shifts in traits of surviving prey.
许多猎物会根据被捕食风险改变自身特征，而这种特征的改变会影响猎物获取资源的速率。因此，捕食者可能对猎物产生“非致命”影响，进而对其他群落成员产生间接影响。这种间接相互作用被称为性状介导的间接相互作用，因为它们源于捕食者对猎物特征的影响，而非猎物密度。由于这种非致命的捕食者效应是即时的，能够影响整个猎物种群，并且可能在猎物的整个生命周期中持续存在，我们认为非致命的捕食者效应很可能对捕食者的净间接效应有很大贡献（即非致命效应的强度可能与捕杀猎物所产生的效应相当）。一项实验支持了这一预测，在该实验中，蜻蜓幼虫（大蜓属）捕食者通过对竞争中的美国牛蛙蝌蚪产生非致命影响，对大型美国牛蛙蝌蚪产生的间接效应，相对于小型蝌蚪密度降低（致命效应）所导致的间接效应而言是巨大的。独立操纵大蜓致命和非致命效应的处理表明，对于一系列不同的致命和非致命效应组合，这一结果都是可靠的。由于许多（即便不是大多数）猎物会根据捕食者改变自身特征，我们的研究结果表明，两个物种之间相互作用系数的大小可能常常与其他群落成员的变化动态相关，而且许多先前归因于捕食者致命效应的间接效应，可能实际上是由于存活猎物的特征变化所致。
