Data from: Nest predation risk explains variation in avian clutch size

Questions about the ecological drivers of, and mechanistic constraints on, productivity have driven research on life history evolution for decades. Resource availability and offspring mortality are considered among the two most important influences on the number of offspring per reproductive attempt. We used a factorial experimental design to manipulate food abundance and perceived offspring predation risk in a wild avian population (red-faced warblers; Cardellina rubrifrons) to identify the mechanistic cause of variation in avian clutch size. Additionally, we tested whether female quality helped explain the extant variation in clutch size. We found no support for the Food Limitation or Female Quality Hypotheses, but we did find support for both predictions of the Nest Predation Risk Hypothesis. Females that experienced an experimentally heightened perception of offspring predation risk responded by laying a smaller clutch than females in the control group. Additionally, predation rates at artificial nests were highest where red-faced warbler clutch size was smallest (at high elevations). Life history theory predicts that an individual should invest less in reproduction when high nest predation risk reduces the likely benefit from that nesting attempt, and indeed we found that birds exhibit phenotypic plasticity in clutch size by laying fewer eggs in response to increasing nest predation risk.数十年来，有关生产力的生态驱动因子与机制约束的研究议题，一直推动着生活史演化（life history evolution）领域的学术探索。资源可获得性与后代死亡率被视为调控单次繁殖尝试后代产出量的两大核心因素。我们采用析因实验设计（factorial experimental design），对野生红脸林莺（Cardellina rubrifrons）种群的食物丰度与个体感知到的后代捕食风险进行操控，以阐明鸟类窝卵数（clutch size）变异的机制性成因。此外，我们检验了雌性个体质量是否能够解释窝卵数现存的自然变异。本研究未发现支持食物限制假说（Food Limitation Hypothesis）与雌性质量假说（Female Quality Hypotheses）的实验证据，但成功验证了巢捕食风险假说（Nest Predation Risk Hypothesis）的两项预测。实验中被强化后代捕食风险感知的雌性个体，其产窝卵数较对照组雌性更低。此外，人工巢捕食率在红脸林莺窝卵数最小的区域——高海拔区域——最高。生活史理论预测，当高巢捕食风险降低某次筑巢尝试的潜在收益时，个体应缩减繁殖投入；本研究结果证实，鸟类会通过减少产卵量来响应升高的巢捕食风险，表现出窝卵数的表型可塑性（phenotypic plasticity）。