Graduate School of Environmental Science, Hokkaido University, Tomakomai, Hokkaido, Japan.
Tenryu Field, Center for Education and Research in Field Sciences, Faculty of Agriculture, Shizuoka University, Hamamatsu, Shizuoka, Japan.
J Anim Ecol. 2020 Jul;89(7):1615-1627. doi: 10.1111/1365-2656.13210. Epub 2020 Apr 4.
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. Reassignment 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.
大多数肉食动物在个体发育过程中都会经历从较小猎物到较大猎物的食性转变。生长中的肉食动物与较大猎物之间的营养关系代表了一种具有大小结构的捕食者-猎物相互作用。这种相互作用的强度部分取决于较小的捕食者体型类群中的个体被招募到较大的捕食者体型类群中。因此，研究较大的猎物如何改变较小的捕食者体型类群向较大的捕食者体型类群的招募情况是很有趣的，因为这会影响它们自己未来的捕食风险。过去的实证研究仅记录到，大型猎物通过降低较小捕食者的生长和/或生存来减少捕食者的招募。在这项研究中，我们提供了相反模式的实证证据：尽管大型猎物增加了较小捕食者的同类相食死亡率，但它们仍会促进较小捕食者向较大捕食者的招募。我们通过研究捕食性蝾螈幼虫 Hynobius retardatus 和它们的大型猎物青蛙蝌蚪 Rana pirica 之间的营养关系来做到这一点。在一个实验中，蝾螈幼虫暴露在有或没有大型青蛙蝌蚪的情况下，我们发现有青蛙蝌蚪存在的情况下，更大的蝾螈出现的数量比没有的情况下多。在随后的实验期间，将青蛙蝌蚪（分配到两个处理组中）重新分配表明，有青蛙蝌蚪存在时，巨型蝾螈的大量出现导致蝾螈对青蛙蝌蚪的捕食加剧。在一个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虫之间的同类相食行为。该实验表明，青蛙蝌蚪在蝾螈幼虫孵化阶段加剧了蝾螈幼虫的同类相食行为，从而使更多的蝾螈幼虫成为大型捕食者。我们的结果表明，青蛙蝌蚪通过加剧捕食性蝾螈幼虫之间的同类相食相互作用，无意中加剧了它们自己未来的捕食风险，从而增强了捕食者向较大体型类群的招募程度。因此，大型猎物可以促进较小的捕食者体型类群中的个体向较大的捕食者体型类群的招募。
