Winkler David W
Museum of Vertebrate Zoology and Department of Zoology, University of California, Berkeley, CA, 94720.
Evolution. 1985 May;39(3):667-677. doi: 10.1111/j.1558-5646.1985.tb00403.x.
In the thirty-five years since David Lack first highlighted the importance of clutch size, a large number of hypotheses have been proposed relating clutch size variation to various environmental and demographic factors. Despite a great deal of both empirical and theoretical work on clutch size, there has been very little effort to test many of the competing hypotheses in explaining a clutch size difference between two populations of the same species. I have taken the latter approach in an effort to explain a clutch size reduction in the California Gull (Larus californicus) population at Mono Lake, California. I compared the breeding biologies of the gulls at Mono Lake and at Great Salt Lake, Utah, collecting data for three breeding seasons at Mono Lake and one breeding season at Great Salt Lake. These data included measurements of the conditions of 60 adults, growth and mortality measurements for approximately 900 chicks, 4450 nest-hours of parental care observations, and the results of egg-removal experiments on 40 females. I tested seven hypotheses to explain the clutch size reduction: age structure, egg predation, bet-hedging, effort reallocation, most productive brood size, parental mortality, and pre-egg food limitation. Each of these hypotheses is described in detail in the introduction. The pre-egg food limitation hypothesis is best able to explain the clutch size reduction at Mono Lake, although the egg-removal experiments show that the resource limitation is relative and not absolute. Clutch size variation at each site need not be viewed as the result of fine-scaled evolutionary adjustment, although the general clutch size decision machinery is presumably molded by selection. Future research must focus on the details of this clutch size decision machinery and its application to the concept of reproductive effort.
自大卫·拉克首次强调窝卵数的重要性以来的35年里，已经提出了大量假说，将窝卵数的变化与各种环境和人口统计学因素联系起来。尽管针对窝卵数进行了大量的实证和理论研究，但在解释同一物种两个种群之间的窝卵数差异时，很少有人努力去检验众多相互竞争的假说。我采用了后一种方法来解释加利福尼亚州莫诺湖的加利福尼亚鸥（Larus californicus）种群窝卵数的减少。我比较了莫诺湖和犹他州大盐湖的海鸥繁殖生物学，收集了莫诺湖三个繁殖季节和大盐湖一个繁殖季节的数据。这些数据包括60只成年海鸥的状况测量、约900只雏鸟的生长和死亡率测量、4450个巢时的亲代抚育观察，以及对40只雌性海鸥进行的移卵实验结果。我检验了七个假说来解释窝卵数的减少：年龄结构、卵捕食、风险分摊、努力重新分配、最具生产力的窝卵数、亲代死亡率和产卵前食物限制。这些假说在引言中都有详细描述。产卵前食物限制假说最能解释莫诺湖窝卵数的减少，尽管移卵实验表明资源限制是相对的而非绝对的。每个地点的窝卵数变化不一定被视为精细尺度进化调整的结果，尽管一般的窝卵数决策机制大概是由选择塑造的。未来的研究必须聚焦于这种窝卵数决策机制的细节及其在繁殖努力概念中的应用。
