Department of Biology, Case Western Reserve University, Cleveland, Ohio, 44106, USA.
Hathaway Brown School, Shaker Heights, Ohio, 44122, USA.
Ecology. 2018 Jan;99(1):224-230. doi: 10.1002/ecy.2056. Epub 2017 Nov 27.
Organisms with complex life cycles commonly exhibit adaptive plasticity in the timing of transitions between life stages. While the threat of predation is predicted to induce earlier transitions, empirical support has been equivocal. When predation risk affects both the propensity to transition to the next life stage and the ability to reach the energetic thresholds necessary to complete the transition, only those individuals in the best physiological condition may be able to accelerate development and emerge earlier. To test this hypothesis, we followed uniquely marked dragonfly larvae (Pachydiplax longipennis) through emergence in pools where we factorially manipulated the presence of a large heterospecific predator (Anax junius) and cannibalism risk via conspecific size variation. Consistent with our hypothesis, high-condition larvae were more likely to emerge in the presence of the heterospecific predator than in its absence, and low-condition larvae were more likely to emerge in its absence than in its presence. Moreover, high-condition larvae emerged earlier when cannibalism risk was high than when it was low. Predation risk therefore has condition-dependent effects on emergence. As predation risk frequently affects resource accumulation, similar mechanisms across taxa could commonly underlie the incongruence between empirical results and theoretical expectations for predator-induced life-history variation.
具有复杂生命周期的生物通常在生命阶段之间的转变时间上表现出适应性可塑性。虽然捕食的威胁预计会促使转变提前发生，但经验证据一直存在争议。当捕食风险影响到向下一生命阶段转变的倾向和达到完成转变所需的能量阈值的能力时，只有那些生理状况最佳的个体才能加速发育并提前出现。为了验证这一假设，我们跟踪了独特标记的蜻蜓幼虫（Pachydiplax longipennis）在池塘中的出现情况，在这些池塘中，我们通过同种大小的变化，对大型异源捕食者（Anax junius）的存在和同类相食风险进行了因子操纵。与我们的假设一致，高条件的幼虫在有异性捕食者存在的情况下比在没有捕食者存在的情况下更有可能出现，而低条件的幼虫在没有捕食者存在的情况下比在有捕食者存在的情况下更有可能出现。此外，当同类相食风险较高时，高条件的幼虫比风险较低时更早出现。因此，捕食风险对出现有条件影响。由于捕食风险经常影响资源积累，类似的机制在不同分类群中可能普遍存在于经验结果与理论预期之间的不一致性，即捕食者诱导的生活史变化。
