In heterogenous environments, predation risk from multiple predators and the availability of resources fluctuate both spatially and temporally. The various predators may include both aerial and terrestrial species that can facilitate each other and present qualitatively different risks to prey. Animals therefore forage across a complex landscape of fear, with areas of risks and relative safety where resources are generally asymmetrically distributed. Therefore, a trade-off exists between remaining safe and locating food. Animals make foraging decisions regarding where, when and for how long to forage by titrating marginal costs and benefits of foraging within and the marginal value of foraging across depletable resource patches. We conducted a series of titration experiments to determine how Allenby’s gerbils (Gerbillus andersoni allenbyi) titrated food and safety when presented with predation risk from owls, vipers and the joint risk from both predators. We manipulated bush and open microhabitats by increasing food availability in the riskier patches. In response to the different levels of enrichment, gerbils titrated food and safety. Riskier open microhabitats needed to be four times as rich in food as bush patches to be of equal value when subjected to predation from owls and the joint risk from owls and vipers. In response to vipers alone, riskier bush patches needed to be 2–4 times as rich in food as safer open patches for the marginal value of foraging to equalize across microhabitats. Overall, predation risk from owls and the joint risk from owls and vipers resulted in the greatest foraging costs for gerbils in risky microhabitats. Thus, the combined overall risk from multiple predator species was equivalent to the risk presented by the gerbils’ most dangerous predator (owls alone). Animals trade-off remaining safe with locating food by titrating the marginal costs and benefits of foraging. We assessed how foragers titrate these costs and benefits through behavioural titration experiments. In our study, gerbils titrated food and safety in response to owls and vipers, aerial and terrestrial predators known to facilitate one another. Riskier patches needed to be 2–4 times as rich in food as safer patches to be of equal value to foraging gerbils. From the gerbils’ perspective, owls are more formidable predators than vipers; despite the facilitation that occurs between these predators, the combination of the two predators had little effect on the titration beyond that of the owls alone. Behavioural titrations are important for quantifying differences in foraging costs between microhabitats and in response to multiple predators with different hunting strategies. As single-predator systems are relatively rare, titration experiments provide the opportunity to gain insights into the foraging/safety trade-offs made by animals in response to multiple predators on the landscape.

中文翻译：

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艾伦比沙鼠如何调整风险和回报以应对不同的捕食者？

在异质环境中，来自多个捕食者的捕食风险和资源的可用性在空间和时间上都有波动。各种捕食者可能包括空中和陆生物种，它们可以相互促进，并对猎物呈现不同的风险。因此，动物在复杂的恐惧环境中觅食，在风险和相对安全的区域中，资源通常分布不对称。因此，在保持安全和定位食物之间存在权衡。动物通过滴定在可耗尽资源斑块内觅食的边际成本和收益以及觅食的边际价值，来决定何时、何时和多长时间觅食。我们进行了一系列滴定实验，以确定当面临猫头鹰、毒蛇的捕食风险以及两种掠食者的共同风险时，艾伦比沙鼠 (Gerbillus andersoni allenbyi) 如何滴定食品和安全。我们通过增加风险较高地区的食物供应来操纵灌木和开放的微生境。为了应对不同程度的富集，沙鼠会滴定食品和安全。当受到猫头鹰的捕食以及猫头鹰和毒蛇的共同威胁时，风险较高的开放式微栖息地的食物含量需要是灌木丛的四倍，才能具有同等价值。仅针对毒蛇，风险较高的灌木丛需要比更安全的开放式斑块的食物丰富 2-4 倍，才能保证觅食的边际价值，以平衡微生境。全面的，猫头鹰的捕食风险以及猫头鹰和毒蛇的共同风险导致沙鼠在危险的微生境中的觅食成本最高。因此，来自多种捕食者物种的综合风险相当于沙鼠最危险的捕食者（仅猫头鹰）所带来的风险。动物通过调整觅食的边际成本和收益来平衡寻找食物的安全性。我们评估了觅食者如何通过行为滴定实验来滴定这些成本和收益。在我们的研究中，沙鼠根据猫头鹰和毒蛇、已知会相互促进的空中和陆地捕食者来调整食物和安全性。要与觅食沙鼠具有同等价值，风险较高的斑块的食物含量是安全斑块的 2-4 倍。从沙鼠的角度来看，猫头鹰是比毒蛇更强大的捕食者。尽管在这些捕食者之间发生了促进作用，但这两种捕食者的结合对滴定的影响很小，超出了猫头鹰单独的影响。行为滴定对于量化微生境之间觅食成本的差异以及对具有不同狩猎策略的多个捕食者的反应非常重要。由于单一捕食者系统相对罕见，滴定实验提供了深入了解动物为应对景观上的多个捕食者而做出的觅食/安全权衡的机会。行为滴定对于量化微生境之间觅食成本的差异以及对具有不同狩猎策略的多个捕食者的反应非常重要。由于单一捕食者系统相对罕见，滴定实验提供了深入了解动物为应对景观上的多个捕食者而做出的觅食/安全权衡的机会。行为滴定对于量化微生境之间觅食成本的差异以及对具有不同狩猎策略的多个捕食者的反应非常重要。由于单一捕食者系统相对罕见，滴定实验提供了深入了解动物为应对景观上的多个捕食者而做出的觅食/安全权衡的机会。