Department of Ecology, Swedish University of Agricultural Sciences, Box 7044, 75007, Uppsala, Sweden,
Oecologia. 2014 Jan;174(1):139-50. doi: 10.1007/s00442-013-2763-z. Epub 2013 Sep 7.
Seasonal fitness declines are common, but the relative contribution of different reproductive components to the seasonal change in the production of reproductive young, and the component-specific drivers of this change is generally poorly known. We used long-term data (17 years) on breeding time (i.e. date of first egg laid) in northern wheatears (Oenanthe oenanthe) to investigate seasonal reproductive patterns and estimate the relative contributions of reproductive components to the overall decline in reproduction, while accounting for factors potentially linked to seasonal declines, i.e. individual and habitat quality. All reproductive components-nest success (reflecting nest predation rate), clutch size, fledging success and recruitment success-showed a clear decline with breeding time whereas subsequent adult survival did not. A non-linear increase in nest predation rate caused nest success to decline rapidly early in the season and level off at ~80% success late in the breeding season. The combined seasonal decline in all reproductive components caused the mean production of recruits per nest to drop from around 0.7-0.2; with the relative contribution greatest for recruitment success which accounted for ~50% of the decline. Our data suggest that changing environmental conditions together with effects of nest predation have strong effects on the seasonal decline in fitness. Our demonstration of the combined effects of all reproductive components and their relative contribution shows that omitting data from later stages of breeding (recruitment) can greatly underestimate seasonal fitness declines.
季节性适应能力下降很常见，但不同繁殖成分对繁殖幼鸟产量季节性变化的相对贡献，以及导致这种变化的特定成分的驱动因素通常知之甚少。我们使用了北方麦鸡（Oenanthe oenanthe）的繁殖时间（即首次产卵日期）的长期数据（17 年），以调查季节性繁殖模式，并估计繁殖成分对繁殖总体下降的相对贡献，同时考虑到与季节性下降相关的因素，即个体和栖息地质量。所有繁殖成分——巢成功率（反映巢捕食率）、窝卵数、育雏成功率和补充繁殖成功率——随着繁殖时间的推移呈明显下降趋势，而随后的成鸟存活率并没有。巢捕食率的非线性增加导致巢成功率在季节早期迅速下降，并在繁殖季节后期稳定在约 80%的成功率。所有繁殖成分的季节性综合下降导致每窝补充繁殖成功率从 0.7-0.2 左右下降；补充繁殖成功率的相对贡献最大，占下降的约 50%。我们的数据表明，环境条件的变化以及巢捕食的影响对适应能力的季节性下降有强烈影响。我们对所有繁殖成分的综合影响及其相对贡献的证明表明，忽略繁殖后期（补充繁殖）的数据会大大低估季节性适应能力下降。
