LEESA, Groupe Ecologie et Conservation, Université d'Angers, Angers, France.
Oecologia. 2012 Jun;169(2):419-30. doi: 10.1007/s00442-011-2218-3. Epub 2011 Dec 27.
Vigilance allows individuals to escape from predators, but it also reduces time for other activities which determine fitness, in particular resource acquisition. The principles determining how prey trade time between the detection of predators and food acquisition are not fully understood, particularly in herbivores because of many potential confounding factors (such as group size), and the ability of these animals to be vigilant while handling food. We designed a fertilization experiment to manipulate the quality of resources, and compared awareness (distinguishing apprehensive foraging and vigilance) of wild impalas (Aepyceros melampus) foraging on patches of different grass height and quality in a wilderness area with a full community of predators. While handling food, these animals can allocate time to other functions. The impalas were aware of their environment less often when on good food patches and when the grass was short. The animals spent more time in apprehensive foraging when grass was tall, and no other variable affected apprehensive behavior. The probability of exhibiting a vigilance posture decreased with group size. The interaction between grass height and patch enrichment also affected the time spent in vigilance, suggesting that resource quality was the main driver when visibility is good, and the risk of predation the main driver when the risk is high. We discuss various possible mechanisms underlying the perception of predation risk: foraging strategy, opportunities for scrounging, and inter-individual interference. Overall, this experiment shows that improving patch quality modifies the trade-off between vigilance and foraging in favor of feeding, but vigilance remains ultimately driven by the visibility of predators by foragers within their feeding patches.
警惕性可以使个体逃避捕食者，但它也会减少其他活动的时间，而这些活动决定了个体的适应性，特别是资源获取。猎物在发现捕食者和获取食物之间分配时间的原则尚未完全理解，尤其是在草食动物中，因为存在许多潜在的混杂因素（例如群体大小），以及这些动物在处理食物时保持警惕的能力。我们设计了一个受精实验来操纵资源质量，并在一个有完整捕食者社区的荒野地区，比较了不同草高和质量斑块中觅食的野生大角斑羚（Aepyceros melampus）对环境的警觉性（区分警惕觅食和警惕）。当这些动物在处理食物时，可以将时间分配到其他功能上。当食物质量好和草短时，大角斑羚对环境的警觉性较低。当草很高时，动物会更多地进行警惕觅食，而其他变量则不会影响警惕行为。警惕姿势的出现概率随群体大小而降低。草高和斑块丰度的相互作用也会影响警惕时间，这表明在能见度好的情况下，资源质量是主要驱动力，而当风险高时，捕食风险是主要驱动力。我们讨论了捕食风险感知的各种可能机制：觅食策略、觅食物机会和个体间干扰。总的来说，这个实验表明，改善斑块质量可以改变警惕性和觅食之间的权衡，有利于进食，但警惕性仍然最终由捕食者在其进食斑块中的可见性驱动。
