Most carnivores undergo diet shift from smaller to larger prey items during ontogeny. The trophic relationship between a growing carnivore and larger prey is representative of a size-structured predator-prey interaction. The strength of this interaction is, in part, determined by the recruitment of individuals from smaller predatory size classes into larger predatory size classes. Therefore, it is interesting to investigate how larger prey alter the recruitment of smaller predator size classes into larger predator size classes, since this can affect their own future predation risk. Past empirical studies have exclusively documented that large prey reduce predator recruitment by decreasing growth and/or survival of the smaller predators. In this study, we provide empirical evidence of the contrasting pattern: large prey enhance the recruitment of smaller predators into larger predators even though they increase cannibalism mortality of the smaller predators. We have done this here by studying the trophic interaction between predatory salamander larvae (Hynobius retardatus) and the frog tadpoles (Rana pirica) that represent their large prey. In a field experiment in which salamander hatchlings were exposed to the presence or absence of large frog tadpoles, we found that more giant salamanders emerged in the presence of frog tadpoles than in their absence. Re-assignment of frog tadpoles (to both treatments) in the subsequent experimental period showed that the enhanced emergence of giant salamanders in the presence of frog tadpoles leads to the intensification of salamander predation on the frog tadpoles. In an additional laboratory experiment, to better understand the underlying mechanisms, we manipulated both the presence of frog tadpoles and the occurrence of cannibalism between salamander hatchlings. This experiment revealed that frog tadpoles intensify the cannibalism of salamander larvae during their hatchling stage, thus allowing more salamander larvae to become large-sized predators. Our results suggest that frog tadpoles can inadvertently intensify their own future predation risk by intensifying cannibalistic interactions among predatory salamander hatchlings, thereby enhancing the degree of predator recruitment to a larger size class. Hence, large prey can enhance the recruitment of individuals from small predator size classes into larger predator size classes.

中文翻译：

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在大型猎物面前加强对大型捕食者的招募

大多数食肉动物在个体发育过程中经历了从较小到较大猎物的饮食转变。成长中的食肉动物和更大的猎物之间的营养关系代表了大小结构的捕食者-猎物相互作用。这种相互作用的强度部分取决于将个体从较小的掠食性尺寸类别招募到较大的掠食性尺寸类别。因此，有趣的是调查较大的猎物如何将较小的捕食者尺寸类别的招募改变为较大的捕食者尺寸类别，因为这会影响它们自己未来的捕食风险。过去的实证研究专门记录了大型猎物通过减少较小捕食者的生长和/或存活来减少捕食者的招募。在这项研究中，我们提供了对比模式的经验证据：大型猎物会增加小型捕食者向大型捕食者的招募，即使它们会增加小型捕食者的同类相食死亡率。我们在这里通过研究掠食性蝾螈幼虫 (Hynobius 延迟) 和代表它们的大型猎物的青蛙蝌蚪 (Rana pirica) 之间的营养相互作用来做到这一点。在将蝾螈幼崽暴露于大青蛙蝌蚪存在或不存在的现场实验中，我们发现在青蛙蝌蚪存在的情况下出现的巨型蝾螈比不存在的情况多。在随后的实验阶段重新分配青蛙蝌蚪（两种处理）表明，在青蛙蝌蚪存在的情况下，大蝾螈出现的增加导致蝾螈对青蛙蝌蚪的捕食加剧。在额外的实验室实验中，为了更好地理解潜在机制，我们操纵了青蛙蝌蚪的存在和蝾螈幼崽之间自相残杀的发生。该实验表明，青蛙蝌蚪在孵化阶段会加剧蝾螈幼虫的自相残杀，从而使更多的蝾螈幼虫成为大型捕食者。我们的研究结果表明，青蛙蝌蚪可以通过加强掠食性蝾螈幼崽之间的同类相食相互作用，从而在更大的规模级别上增加捕食者的招募程度，从而在不经意间加剧了它们自己未来的捕食风险。因此，大型猎物可以促进个体从小捕食者体型到更大捕食者体型的招募。我们操纵了青蛙蝌蚪的存在和蝾螈幼崽之间自相残杀的发生。该实验表明，青蛙蝌蚪在孵化阶段会加剧蝾螈幼虫的自相残杀，从而使更多的蝾螈幼虫成为大型捕食者。我们的研究结果表明，青蛙蝌蚪可以通过加强掠食性蝾螈幼崽之间的同类相食相互作用，从而在更大的规模级别上增加捕食者的招募程度，从而在不经意间加剧了它们自己未来的捕食风险。因此，大型猎物可以促进个体从小捕食者体型到更大捕食者体型的招募。我们操纵了青蛙蝌蚪的存在和蝾螈幼崽之间自相残杀的发生。这项实验表明，青蛙蝌蚪在孵化阶段会加剧蝾螈幼虫的自相残杀，从而使更多的蝾螈幼虫成为大型捕食者。我们的研究结果表明，青蛙蝌蚪可以通过加强掠食性蝾螈幼崽之间的同类相食相互作用，从而在更大的规模级别上增加捕食者的招募程度，从而在不经意间加剧了它们自己未来的捕食风险。因此，大型猎物可以促进个体从小捕食者体型到更大捕食者体型的招募。从而让更多的蝾螈幼虫成为大型捕食者。我们的研究结果表明，青蛙蝌蚪可以通过加强掠食性蝾螈幼崽之间的同类相食相互作用，从而在更大的规模级别上增加捕食者的招募程度，从而在不经意间加剧了它们自己未来的捕食风险。因此，大型猎物可以促进个体从小捕食者体型到更大捕食者体型的招募。从而让更多的蝾螈幼虫成为大型捕食者。我们的研究结果表明，青蛙蝌蚪可以通过加强掠食性蝾螈幼崽之间的同类相食相互作用，从而在更大的规模级别上增加捕食者的招募程度，从而在不经意间加剧了它们自己未来的捕食风险。因此，大型猎物可以促进个体从小捕食者体型到更大捕食者体型的招募。