Department of Ecology, Swedish University of Agricultural Sciences, Box 7044, SE-75007, Uppsala, Sweden.
Ecology. 2017 Aug;98(8):2102-2110. doi: 10.1002/ecy.1891. Epub 2017 Jun 28.
The seasonal timing of reproduction is a major fitness factor in many organisms. Commonly, individual fitness declines with time in the breeding season. We investigated three suggested but rarely tested hypotheses for this seasonal fitness decline: (1) time per se (date hypothesis), (2) late breeders are of lower quality than early ones (individual quality hypothesis), and (3) late breeders are breeding at poorer territories than early breeders (territory quality hypothesis). We used Bayesian variance component analyses to examine reproductive output (breeding success, number fledged, and number of recruits) from repeated observations of female Northern Wheatears (Oenanthe oenanthe) and individual territories from a 20-yr population study. The major part of the observed seasonal decline in reproductive output seemed to be driven by date-related effects, whereas female age and territory type (i.e., known indicators of temporary quality) contributed to a smaller degree. Other, persistent effects linked to individual and territory identity did not show any clear patterns on the seasonal decline in reproductive output. To better disentangle the quality effects (persistent and temporary) of individual and territory from effects caused by the deterioration of the environment we suggest a protocol combining experimental manipulation of breeding time with a variance-covariance partitioning method used here.
繁殖的季节性时间是许多生物的主要适应因素。通常，个体在繁殖季节随着时间的推移而适应度下降。我们调查了三种很少被测试的季节性适应度下降的假设：（1）时间本身（日期假说），（2）晚育者的质量低于早育者（个体质量假说），（3）晚育者在较劣的领地繁殖，而不是早育者（领地质量假说）。我们使用贝叶斯方差分量分析，从对 20 年种群研究中重复观察到的雌性北方麦鸡（Oenanthe oenanthe）和个体领地的繁殖输出（繁殖成功率、育雏数和新繁殖个体数）进行分析。观察到的繁殖输出季节性下降的主要部分似乎是由与日期相关的效应驱动的，而雌性年龄和领地类型（即临时质量的已知指标）的贡献较小。与个体和领地身份相关的其他持久效应在繁殖输出的季节性下降中没有表现出任何明显的模式。为了更好地区分个体和领地的质量效应（持久和临时）与环境恶化引起的效应，我们建议结合繁殖时间的实验操作和这里使用的方差协方差分解方法的协议。
