Brommer Jon E, Pietiäinen Hannu, Kokko Hanna
Division of Population Biology, Department of Ecology and Systematics, PO Box 17 (Arkadiankatu 7), FIN-00014, University of Helsinki, Finland.
Proc Biol Sci. 2002 Mar 22;269(1491):647-54. doi: 10.1098/rspb.2001.1929.
Plastic life-history traits can be viewed as adaptive responses to environmental conditions, described by a reaction norm. In birds, the decline in clutch size with advancing laying date has been viewed as a reaction norm in response to the parent's own (somatic or local environmental) condition and the seasonal decline in its offspring's reproductive value. Theory predicts that differences in the seasonal recruitment are mirrored in the seasonal decrease in clutch size. We tested this prediction in the Ural owl. The owl's main prey, voles, show a cycle of low, increase and peak phases. Recruitment probability had a humped distribution in both increase and peak phases. Average recruitment probability was two to three times higher in the increase phase and declined faster in the latter part of the season when compared with the peak phase. Clutch size decreased twice as steep in the peak (0.1 eggs day-1) as in the increase phase (0.05 eggs day-1). This result appears to refute theoretical predictions of seasonal clutch size declines. However, a re-examination of current theory shows that the predictions of modelling are less robust to details of seasonal condition accumulation in birds than originally thought. The observed pattern can be predicted, assuming specifically shaped seasonal increases in condition across individuals.
可塑性生活史特征可被视为对环境条件的适应性反应，由反应规范来描述。在鸟类中，窝卵数随产卵日期推进而减少被视为一种反应规范，以应对亲鸟自身的（躯体或局部环境）状况及其后代繁殖价值的季节性下降。理论预测，季节性补充的差异反映在窝卵数的季节性减少上。我们在乌林鸮中检验了这一预测。乌林鸮的主要猎物田鼠呈现出数量低、增加和峰值阶段的循环。在增加阶段和峰值阶段，补充概率均呈驼峰分布。与峰值阶段相比，增加阶段的平均补充概率高出两到三倍，且在季节后期下降得更快。窝卵数在峰值阶段（0.1枚卵/天）下降的速度是增加阶段（0.05枚卵/天）的两倍。这一结果似乎反驳了窝卵数季节性下降的理论预测。然而，对当前理论的重新审视表明，建模预测对鸟类季节性条件积累细节的稳健性不如最初认为的那样。假设个体间条件呈特定形状的季节性增加，那么观察到的模式是可以预测的。
