Török János, Hegyi Gergely, Tóth László, Könczey Réka
Behavioural Ecology Group, Department of Systematic Zoology and Ecology, Eötvös Loránd University, Pázmány P. sétány 1/C, Budapest, 1117, Hungary.
Oecologia. 2004 Nov;141(3):432-43. doi: 10.1007/s00442-004-1667-3. Epub 2004 Aug 17.
Investment into the current reproductive attempt is thought to be at the expense of survival and/or future reproduction. Individuals are therefore expected to adjust their decisions to their physiological state and predictable aspects of environmental quality. The main predictions of the individual optimization hypothesis for bird clutch sizes are: (1) an increase in the number of recruits with an increasing number of eggs in natural broods, with no corresponding impairment of parental survival or future reproduction, and (2) a decrease in the fitness of parents in response to both negative and positive brood size manipulation, as a result of a low number of recruits, poor future reproduction of parents, or both. We analysed environmental influences on costs and optimization of reproduction on 6 years of natural and experimentally manipulated broods in a Central European population of the collared flycatcher. Based on dramatic differences in caterpillar availability, we classified breeding seasons as average and rich food years. The categorization was substantiated by the majority of present and future fitness components of adults and offspring. Neither observational nor experimental data supported the individual optimization hypothesis, in contrast to a Scandinavian population of the species. The quality of fledglings deteriorated, and the number of recruits did not increase with natural clutch size. Manipulation revealed significant costs of reproduction to female parents in terms of future reproductive potential. However, the influence of manipulation on recruitment was linear, with no significant polynomial effect. The number of recruits increased with manipulation in rich food years and tended to decrease in average years, so control broods did not recruit more young than manipulated broods in any of the year types. This indicates that females did not optimize their clutch size, and that they generally laid fewer eggs than optimal in rich food years. Mean yearly clutch size did not follow food availability, which suggests that females cannot predict food supply of the brood-rearing period at the beginning of the season. This lack of information on future food conditions seems to prevent them from accurately estimating their optimal clutch size for each season. Our results suggest that individual optimization may not be a general pattern even within a species, and alternative mechanisms are needed to explain clutch size variation.
对当前繁殖尝试的投入被认为是以生存和/或未来繁殖为代价的。因此，个体有望根据自身生理状态和环境质量的可预测方面来调整决策。个体优化假说对鸟类窝卵数的主要预测是：（1）在自然育雏中，随着卵数增加，新出生雏鸟数量增加，且亲代生存或未来繁殖没有相应受损；（2）由于新出生雏鸟数量少、亲代未来繁殖能力差或两者兼而有之，对亲代进行负向和正向窝卵数操纵时，亲代的适合度都会降低。我们分析了中欧白领姬鹟种群中6年自然育雏和实验操纵育雏情况下环境对繁殖成本和优化的影响。基于毛虫可获得量的显著差异，我们将繁殖季节分为食物平均年和食物丰富年。这种分类得到了成年个体和后代当前及未来大多数适合度成分的证实。与该物种的斯堪的纳维亚种群不同，观察数据和实验数据均不支持个体优化假说。雏鸟质量下降，新出生雏鸟数量并未随自然窝卵数增加。操纵实验显示，对雌性亲代而言，繁殖在未来繁殖潜力方面存在显著成本。然而，操纵对新出生雏鸟数量的影响是线性的，没有显著的多项式效应。在食物丰富年，新出生雏鸟数量随操纵增加，在食物平均年则趋于减少，所以在任何年份类型中，对照窝的新出生雏鸟数量都不比操纵窝多。这表明雌性没有优化其窝卵数，而且在食物丰富年，它们通常产卵数少于最优数量。平均年窝卵数并不随食物可获得量变化，这表明雌性在繁殖季节开始时无法预测育雏期的食物供应情况。这种对未来食物条件信息的缺乏似乎使它们无法准确估计每个季节的最优窝卵数。我们的结果表明，即使在一个物种内，个体优化也可能不是普遍模式，需要其他机制来解释窝卵数的变化。
