Effects of spring temperatures on the strength of selection on timing of reproduction in a long-distance migratory bird

Climate change has differentially affected the timing of seasonal events for interacting trophic levels, and this has often led to increased selection on seasonal timing. Yet, the environmental variables driving this selection have rarely been identified, limiting our ability to predict future ecological impacts of climate change. Using a dataset spanning 31 years from a natural population of pied flycatchers (Ficedula hypoleuca), we show that directional selection on timing of reproduction intensified in the first two decades (1980–2000) but weakened during the last decade (2001–2010). Against expectation, this pattern could not be explained by the temporal variation in the phenological mismatch with food abundance. We therefore explored an alternative hypothesis that selection on timing was affected by conditions individuals experience when arriving in spring at the breeding grounds: arriving early in cold conditions may reduce survival. First, we show that in female recruits, spring ...

气候变化已对存在相互作用的各营养级（trophic levels）的季节事件发生时间造成差异化影响，这通常会强化针对季节发生时间的选择压力。然而，驱动此类选择的环境变量极少被探明，这极大限制了我们预测气候变化未来生态影响的能力。本研究依托采自斑姬鹟（Ficedula hypoleuca）天然种群、跨度达31年的数据集，结果显示繁殖时间的定向选择（directional selection）在1980年至2000年的前两个十年间显著增强，但在2001年至2010年的最后十年间有所减弱。与预期相悖的是，这一模式无法通过与食物丰度相关的物候错配（phenological mismatch）的时间变化加以解释。因此，我们探索了另一项假说：繁殖时间所受的选择会受到个体春季抵达繁殖地（breeding grounds）时所经历的环境条件影响——在低温环境下提前抵达可能会降低个体存活率。首先，我们针对雌性补充个体（recruits）展开分析，春季……