1. Prey face a trade-off between acquiring food and avoiding predation, but food availability, and therefore its effect, is rarely measured in field studies investigating non-lethal effects of predation. The main aim of this study is to investigate the role of the presence of predators in the functional adjustments of feeding parameters with patch quality in a medium-size herbivore. 2. In Hwange National Park (Zimbabwe), we set up an experiment by manipulating, over two years, patch quality for impala (Aepyceros melampus), a medium-sized herbivore. We assess predation risk by monitoring the presence of three GPS-equipped predators: African lions (Panthera leo), spotted hyaenas (Crocuta crocuta) and African wild dogs (Lycaon pictus). 3. In enriched, fertilised plots the impalas reduced step rates (i.e. the rates of change in feeding stations), and increased their number of bites per feeding station while bite rates were not affected. Thus, the main adjustment of their feeding was the step rate. The total time the impalas spent vigilant appeared to be a good predictor of the variation of their bite rate. Although vigilance caused a reduction in bite rate when at a feeding station, the impalas reduced the relative costs of vigilance by continuing chewing and processing their food when scanning for predators. 4. When predators were in the vicinity, the impalas increased their exclusive vigilance (high-cost vigilance) but not their vigilance while chewing (low-cost vigilance) and decreased their bite rate while their step rate and the number of bites per feeding station did not change significantly. The impalas were thus visually disconnected from their patch, and reduced their bite rate when actually foraging. Exclusive vigilance increased when both lions and hyaenas were in the vicinity, and when wild dogs were nearby. 5. Patterns of vigilance that altered bite rate were linked to the presence of predators during the previous 24h. Over the long term patch quality was the main determinant of the feeding parameters (step rate and bite rate). This study shows how predators, by affecting the time prey devote to predator detection, shape the functional adjustments of food acquisition by prey to local patch quality.

中文翻译：

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解开自下而上和自上而下驱动因素在多个捕食者的食物获取和安全之间的权衡中的作用

1. 猎物面临着获取食物和避免捕食之间的权衡，但在调查捕食的非致命影响的实地研究中，很少测量食物的可用性及其影响。本研究的主要目的是研究捕食者的存在在中型食草动物斑块质量的摄食参数功能调整中的作用。2. 在万基国家公园（津巴布韦），我们进行了一项实验，在两年多的时间里，对黑斑羚（Aepyceros melampus）这种中型食草动物的斑块质量进行了处理。我们通过监测三种配备 GPS 的捕食者的存在来评估捕食风险：非洲狮 (Panthera leo)、斑点鬣狗 (Crocuta crocuta) 和非洲野狗 (Lycaon pictus)。3. 在肥沃、施肥的地块中，黑斑羚降低了步率（即饲喂站的变化率），并增加了每个喂食站的咬伤次数，而咬伤率不受影响。因此，它们进料的主要调整是步进速率。黑斑羚保持警惕的总时间似乎可以很好地预测它们咬合率的变化。尽管在喂食站保持警惕会降低咬伤率，但黑斑羚在寻找捕食者时会继续咀嚼和加工食物，从而降低了保持警惕的相对成本。4.当掠食者在附近时，黑斑羚增加了他们的专属警戒（高成本警戒），而不是他们咀嚼时的警戒（低成本警戒），并降低了它们的咬合率，而它们的步率和每个喂食站的咬伤次数没有显着变化。因此，黑斑羚在视觉上与它们的斑块分离，并在实际觅食时降低了它们的咬合率。当狮子和鬣狗都在附近时，当野狗在附近时，排他性的警惕性就会增加。5. 改变咬合率的警惕模式与过去 24 小时内捕食者的存在有关。从长远来看，贴片质量是喂养参数（步进速率和咬合速率）的主要决定因素。这项研究显示了捕食者如何通过影响猎物用于捕食者检测的时间来塑造猎物获取食物对局部斑块质量的功能调整。从长远来看，贴片质量是喂养参数（步进速率和咬合速率）的主要决定因素。这项研究显示了捕食者如何通过影响猎物用于捕食者检测的时间来塑造猎物获取食物对局部斑块质量的功能调整。从长远来看，贴片质量是喂养参数（步进速率和咬合速率）的主要决定因素。这项研究显示了捕食者如何通过影响猎物用于捕食者检测的时间来塑造猎物获取食物对局部斑块质量的功能调整。