The Seasonal Decline in Avian Clutch Size: Parental Condition or Environmental Deterioration?

鸟类学中最强有力的概括之一就是鸟类 在这个季节晚些时候产卵的企鹅每窝产的蛋会更少。 对于这种模式的原因存在着相当大的分歧。 一种学派认为，季节性衰退是一种非适应性的现象。 女性条件变化的后果，这有一个 对产蛋时间和窝卵数的影响。 的 另一派认为，季节性的窝卵数量下降是一种适应性的变化。 对产蛋雌鼠食物可利用性变化的反应 或季节性下降的养育后代的前景。 是 我建议从三个方面来区分这些可能性。 一个实验将测试食物供应对 降低了觅食的收益率， 女性在产卵前的状况，并寻找预测 铺设时间和离合器大小的变化。 第二个实验 会改变养鸡的时间 如果条件有 对养鸡成功的压倒性影响，然后操纵 不会影响后代的繁衍。 如果在 另一方面，繁殖环境起主导作用， 后代的生产在不同的群体中会有所不同。 统计检验 将收集有关情况、窝卵数和产蛋日期的数据， 通过偏回归分析，寻找显著影响 产蛋日期对窝卵数的影响。 在所有这些测试中，情况将以脂肪和 借助新开发的非破坏性 技术. 这些结果不仅应该引起人们的兴趣， 生理生态学家对身体与环境之间的相互作用 条件和鸟类的历史，而且人口生物学家 对生命史的变异感兴趣

One of the strongest generalizations in ornithology is that birds that lay later in the season tend to lay fewer eggs per clutch. There is considerable disagreement over the causes of this pattern. One school maintains that the seasonal decline is a nonadaptive consequences of variation in female condition, which has an overriding effect both on timing of laying and clutch size. The other school sees seasonal clutch size declines as an adaptive response to variation in food availability for the laying female or seasonally declining prospects for rearing offspring. It is proposed to distinguish between these possibilities in three ways. One experiment will test for the effect of food supply for the laying female by decreasing the foraging profitability and the condition of the female prior to laying and looking for predicted shifts in timing of laying and clutch size. A second experiment will alter the timing of chick-rearing. If condition has the overwhelming effect on chick-rearing success, then the manipulation will have no effect on offspring production across groups. If, on the other hand, the breeding environment has a predominant effect, offspring production will vary across groups. A statistical test will take data on condition, clutch size, and laying date, and, through partial regression analysis, look for a significant effect of laying date on clutch size once condition is controlled for. In all these tests, condition will be measured in terms of fat and protein stores with the aid of newly developed nondestructive techniques. These results should be of interest not only to physiological ecologists interested in the interaction between body condition and avian histories, but also to population biologists interested in life history variation.