University of Colorado Museum of Natural History, Boulder, Colorado 80309, USA.
Ecology. 2013 Jun;94(6):1327-37. doi: 10.1890/12-0953.1.
Explaining latitudinal patterns in life history traits remains a challenge for ecologists and evolutionary biologists. One such prominent pattern is the latitudinal gradient in clutch size in birds: the number of eggs laid in a reproductive bout increases with latitude in many species. One intuitive hypothesis proposes that the longer days at high latitudes during the breeding season allow parents to spend more time foraging each day, which results in greater total food delivery to the brood each day, and hence more offspring produced. This day length hypothesis is virtually untested, although it was proposed nearly 100 years ago. We developed a conceptual framework for distinguishing between the day length hypothesis and the widely accepted alternative hypothesis that attributes the latitudinal gradient in clutch size to increased per capita food resources at higher latitudes. Using this framework to contrast components of reproductive effort and life history patterns in a mid- and high-latitude Tree Swallow (Tachycineta bicolor) population provided clear evidence for the day length hypothesis, but little evidence for the alternative. Our findings suggest that the length of an animal's workday may be an important, but unappreciated, component of reproductive effort.
解释生活史特征的纬度格局仍然是生态学家和进化生物学家面临的挑战。一个突出的模式是鸟类在繁殖季节中产卵数目的纬度梯度：在许多物种中，产卵数随着纬度的增加而增加。一个直观的假设提出，在繁殖季节高纬度地区的较长白天允许父母每天花费更多的时间觅食，这导致每天向雏鸟提供更多的总食物，从而产生更多的后代。尽管该假设几乎没有得到验证，但它是在近 100 年前提出的。我们制定了一个概念框架，用于区分白天长度假说和被广泛接受的替代假说，该假说将卵数的纬度梯度归因于高纬度地区人均食物资源的增加。使用该框架对比中高纬度树燕（Tachycineta bicolor）种群的繁殖努力和生活史模式的组成部分，为白天长度假说提供了明确的证据，但对替代假说的证据很少。我们的研究结果表明，动物的工作日长度可能是繁殖努力的一个重要但未被认识到的组成部分。
