Data and code from: Quantitative analyses of stochastic influences on the response to phenotypic selection in a small passerine, the collared flycatcher

Stochastic influences arising from demographic and environmental
stochasticity strongly affect eco-evolutionary dynamics. Demographic
stochasticity causes reduction in the long-run population growth rates at
small population sizes and generates genetic drift. The effects of
stochastic environmental fluctuations on fitness are more difficult to
assess because it may introduce stochasticity in the selection processes.
Here, we examined stochastic variation in the response to selection on
three breeding parameters in a collared flycatcher (Ficedula albicollis)
population using density-dependent and frequency-dependent environmental
covariances among individuals with different phenotypes. Environmental
fluctuations induced considerable variation among individual fitness
dependent on their phenotype and population size. These stochastic effects
on fitness were strongest for individuals with large clutches or few
fledglings, and in years with few conspecifics. Contrastingly, we found no
evidence that the stochastic environmental effects on individual fitness
varied with laying date. Furthermore, we found that phenotype-specific
effects of environmental fluctuations were less correlated for fledgling
number than for laying date and clutch size, resulting in less correlation
in fitness between pairs with similar fledgling numbers. Our analyses
showed that the stochastic component in the response to selection on
clutch size and laying date caused by environmental stochasticity at the
carrying capacity was of the same order as the component due to genetic
drift. This means that stochasticity can affect phenotypic evolution even
in large populations via stochastic selection generated by environmental
fluctuations.

由种群统计学随机性与环境随机性共同引发的随机扰动，会对生态-进化动态产生强烈影响。种群统计学随机性会导致小种群规模下的长期种群增长率下降，并引发遗传漂变（genetic drift）。环境随机波动对适合度的影响更难评估，因为这类波动可能会在选择过程中引入随机性。
本研究针对斑姬鹟（*Ficedula albicollis*）种群中的3个繁殖参数的选择响应展开分析，通过不同表型个体间的密度依赖与频率依赖环境协方差，探究了其中的随机变异。环境波动会引发个体适合度出现显著差异，且该差异取决于个体表型与种群规模。这类对适合度的随机扰动，在窝卵数较多、离巢幼鸟较少的个体，以及同种个体数量稀少的年份中表现最为显著。
与之相反，本研究未发现环境随机扰动对个体适合度的影响会随产卵日期发生变化的证据。此外，相较于产卵日期与窝卵数，环境波动对不同表型个体的影响在离巢幼鸟数量上的相关性更低，这使得离巢幼鸟数量相近的个体对之间的适合度相关性也更低。
本研究的分析结果显示，在环境容纳量水平下，由环境随机性引发的、针对窝卵数与产卵日期的选择响应中的随机组分，其量级与遗传漂变带来的随机组分相当。这意味着，即便在大型种群中，随机性也可通过环境波动引发的随机选择，对表型进化产生影响。