Phenotypic plasticity in response to fine-grained environmental variation in predation.

1. In nature, organisms experience environmental variability at coarse-grained (inter-generational) and fine-grained (intra-generational) scales and a common response to environmental variation is phenotypic plasticity. The emphasis of most empirical work on plasticity has been on examining coarse-grained variation with the goal of understanding the costs and benefits of plastic responses in response to a particular environment. 2. In this study, we investigated the effects of fine-grained variation in predation on the inducible defences of larval wood frogs (Rana sylvatica) by widely altering the density and feeding schedule of caged predators (Dytiscusspp.) while holding average predation constant. 3. We found that predator cues induced change in tadpole behaviour, morphology, and mass. Surprisingly, however, temporal variation in predation did not cause the tadpoles to alter their activity (compared to a constant predation treatment) or mass. Temporal variation in predation did alter tadpole tail depth, but only when experiencing our most extreme variation treatment in which the predators were fed once every 8 days. Under these conditions, the predator-induced tadpole tail was less extreme compared to environments containing constant predation. 4. While a number of previous studies have examined behavioural responses of prey to temporal variation in predation risk without holding average predation constant, this appears to be the first test of temporal variation per se. As in previous studies of organism responses to temporal variation in resources, our results suggest that fine-grained environmental variability can affect the expression of phenotypically plastic traits, but our tadpoles appear to be generally unresponsive to this finegrained variation for many of their traits.

1. 自然界中，生物会在粗尺度（代际间）与细尺度（代内）层面遭遇环境波动，而应对环境变化的常见策略为表型可塑性（phenotypic plasticity）。当前绝大多数关于可塑性的实证研究均聚焦于粗尺度环境波动，旨在阐明特定环境下塑性响应的成本与收益。
2. 本研究通过大幅改变笼养捕食者（龙虱属（Dytiscus spp.））的种群密度与投喂节律，同时维持平均捕食压力恒定，探究了细尺度捕食波动对林蛙（Rana sylvatica）幼体诱导防御（inducible defences）的影响。
3. 研究结果显示，捕食者线索可诱导蝌蚪的行为、形态与体重发生改变。但令人意外的是，捕食压力的时间波动并未使蝌蚪的活动水平（相较于恒定捕食处理组）或体重发生改变。捕食压力的时间波动仅在我们采用的极端波动处理（即捕食者每8天投喂一次）下，才会改变蝌蚪的尾深；在此条件下，由捕食者诱导产生的蝌蚪尾部发育程度相较于恒定捕食环境下的个体更低。
4. 尽管此前已有多项研究在未维持平均捕食压力恒定的前提下，探究了猎物对捕食风险时间波动的行为响应，但本研究似乎是首个直接针对捕食压力时间波动本身开展的检验。与此前关于生物对资源时间波动响应的研究结果一致，本研究结果表明，细尺度环境波动可影响表型可塑性性状的表达，但林蛙幼体对多数性状而言，似乎并未对这类细尺度环境波动产生明显应答。