Data from: Multiple extreme climatic events strengthen selection for earlier breeding in a wild passerine

Global climate warming results in an increase in mean temperatures and in the frequency of extreme climatic events (ECEs), which could both strongly impact ecosystems and populations. Most studies assessing the impact of global warming on ecosystems have focused on warming trends while neglecting ECEs. In particular, the effects of multiple ECEs on fitness, and their consequences for selection, are still missing. Here we explored the effects of daily extreme rainfalls, as well as the occurrence of extremely hot and cold days, on clutch size and laying date in a wild blue tit population (Cyanistes caeruleus) monitored over 25 years. During the nestling phase (8–15 days old), the number of fledglings in a brood was negatively correlated with extremely hot days. The presence of extremely hot days between days 8 and 15 was also associated with an increase in the strength of selection acting on laying date, independently of mean temperature trends during the same period: when 10% of broods in the population experienced this type of ECE, selection for earlier breeding increased by 39%. Our results represent a unique quantification of the impact of multiple ECEs on the fitness landscape and emphasize their role as climatic drivers of selection.

全球气候变暖导致平均气温升高，同时升高了极端气候事件（extreme climatic events, ECEs）的发生频率，二者均可对生态系统及物种种群造成强烈影响。现有评估全球变暖对生态系统影响的研究，大多聚焦于气温变暖趋势，却忽视了极端气候事件的作用。具体而言，目前仍缺乏关于多重极端气候事件对适合度的影响，及其对自然选择产生的后续效应的相关研究。本研究针对一个历经25年监测的野生青山雀（Cyanistes caeruleus）种群，探究了单日极端降雨、极端高温日与极端低温日的发生对其窝卵数与产卵日期的影响。在雏鸟阶段（8至15日龄），一窝的离巢幼鸟数量与极端高温日数呈负相关关系。在雏鸟8至15日龄期间出现极端高温日，还与产卵日期所受自然选择强度的提升显著相关，且这一关联不受同期平均气温变化趋势的影响：当种群中有10%的窝雏经历此类极端气候事件时，提前繁殖的选择强度提升了39%。本研究结果首次量化了多重极端气候事件对适合度景观的影响，并强调了其作为自然选择气候驱动因子的重要作用。