Beckerman A P, Uriarte M, Schmitz O J
Yale University, School of Forestry and Environmental Studies, 370 Prospect Street, New Haven, CT 06511, USA.
Proc Natl Acad Sci U S A. 1997 Sep 30;94(20):10735-8. doi: 10.1073/pnas.94.20.10735.
Predators of herbivorous animals can affect plant populations by altering herbivore density, behavior, or both. To test whether the indirect effect of predators on plants arises from density or behavioral responses in a herbivore population, we experimentally examined the dynamics of terrestrial food chains comprised of old field plants, leaf-chewing grasshoppers, and spider predators in Northeast Connecticut. To separate the effects of predators on herbivore density from the effects on herbivore behavior, we created two classes of spiders: (i) risk spiders that had their feeding mouth parts glued to render them incapable of killing prey and (ii) predator spiders that remained unmanipulated. We found that the effect of predators on plants resulted from predator-induced changes in herbivore behavior (shifts in activity time and diet selection) rather than from predator-induced changes in grasshopper density. Neither predator nor risk spiders had a significant effect on grasshopper density relative to a control. This demonstrates that the behavioral response of prey to predators can have a strong impact on the dynamics of terrestrial food chains. The results make a compelling case to examine behavioral as well as density effects in theoretical and empirical research on food chain dynamics.
食草动物的捕食者可以通过改变食草动物的密度、行为或两者兼而有之来影响植物种群。为了测试捕食者对植物的间接影响是源于食草动物种群的密度还是行为反应，我们通过实验研究了康涅狄格州东北部由荒地植物、咀嚼叶片的蚱蜢和蜘蛛捕食者组成的陆地食物链的动态。为了将捕食者对食草动物密度的影响与对食草动物行为的影响区分开来，我们创建了两类蜘蛛：（i）风险蜘蛛，其进食口器被粘上，使其无法杀死猎物；（ii）捕食者蜘蛛，未进行处理。我们发现，捕食者对植物的影响源于捕食者引起的食草动物行为变化（活动时间和饮食选择的改变），而不是捕食者引起的蚱蜢密度变化。相对于对照组，捕食者蜘蛛和风险蜘蛛对蚱蜢密度均无显著影响。这表明猎物对捕食者的行为反应会对陆地食物链的动态产生强烈影响。这些结果有力地证明了在食物链动态的理论和实证研究中，需要同时考察行为效应和密度效应。
