Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2M9, Canada.
Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, M1C 1A4, Canada.
Ecology. 2018 Aug;99(8):1716-1723. doi: 10.1002/ecy.2381. Epub 2018 Jun 21.
In recent years, it has been argued that the effect of predator fear exacts a greater demographic toll on prey populations than the direct killing of prey. However, efforts to quantify the effects of fear have primarily relied on experiments that replace predators with predator cues. Interpretation of these experiments must consider two important caveats: (1) the magnitude of experimenter-induced predator cues may not be realistically comparable to those of the prey's natural sensory environment, and (2) given functional predators are removed from the treatments, the fear effect is measured in the absence of any consumptive effects, a situation which never occurs in nature. We contend that demographic consequences of fear in natural populations may have been overestimated because the intensity of predator cues applied by experimenters in the majority of studies has been unnaturally high, in some instances rarely occurring in nature without consumption. Furthermore, the removal of consumption from the treatments creates the potential situation that individual prey in poor condition (those most likely to contribute strongly to the observed fear effects via starvation or reduced reproductive output) may have been consumed by predators in nature prior to the expression of fear effects, thus confounding consumptive and fear effects. Here, we describe an alternative treatment design that does not utilize predator cues, and in so doing, better quantifies the demographic effect of fear on wild populations. This treatment substitutes the traditional cue experiment where consumptive effects are eliminated and fear is simulated with a design where fear is removed and consumptive effects are simulated through the experimental removal of prey. Comparison to a natural population would give a more robust estimate of the effect of fear in the presence of consumption on the demographic variable of interest. This approach represents a critical advance in quantifying the mechanistic pathways through which predation structures ecological communities. Discussing the merits of both treatments will motivate researchers to go beyond simply describing the existence of fear effects and focus on testing their true magnitude in wild populations and natural communities.
近年来，有人认为，与直接捕杀猎物相比，捕食者的恐惧对猎物种群造成的人口统计学影响更大。然而，量化恐惧影响的努力主要依赖于用捕食者线索代替捕食者的实验。解释这些实验必须考虑两个重要的警告：（1）实验者诱导的捕食者线索的强度可能与猎物自然感觉环境中的强度不具有现实可比性；（2）由于功能上的捕食者从处理中被移除，恐惧效应是在没有任何消耗效应的情况下测量的，而这种情况在自然界中从未发生过。我们认为，由于实验者在大多数研究中应用的捕食者线索的强度异常高，在某些情况下，即使没有消耗，自然界中也很少出现这种情况，因此自然种群中恐惧的人口统计学后果可能被高估了。此外，从处理中消除消耗会产生一种潜在情况，即处于不良状态的个体猎物（那些最有可能因饥饿或繁殖输出减少而强烈导致观察到的恐惧效应的个体）可能在恐惧效应表达之前就被自然界中的捕食者消耗掉了，从而混淆了消耗和恐惧效应。在这里，我们描述了一种替代处理设计，该设计不使用捕食者线索，因此更好地量化了恐惧对野生种群的人口统计学影响。这种处理方法用实验去除猎物来替代传统的利用消耗效应消除捕食者线索并模拟恐惧的实验设计，从而模拟恐惧效应，同时模拟消耗效应。与自然种群进行比较，将更准确地估计在存在消耗的情况下恐惧对感兴趣的人口统计学变量的影响。这种方法代表了量化捕食作用构建生态群落的机制途径的重要进展。讨论这两种处理方法的优点将激励研究人员不仅仅描述恐惧效应的存在，而是专注于在野生种群和自然群落中测试它们的真实规模。
