Department of Animal Behaviour, Bielefeld University, 33615 Bielefeld, Germany;
Research Group Behavioural Genetics and Evolutionary Ecology, Max Planck Institute for Ornithology, 82319 Seewiesen, Germany.
Proc Natl Acad Sci U S A. 2017 Jul 3;114(27):E5474-E5481. doi: 10.1073/pnas.1620043114. Epub 2017 Jun 20.
Adult sex ratio (ASR) is a central concept in population biology and a key factor in sexual selection, but why do most demographic models ignore sex biases? Vital rates often vary between the sexes and across life history, but their relative contributions to ASR variation remain poorly understood-an essential step to evaluate sex ratio theories in the wild and inform conservation. Here, we combine structured two-sex population models with individual-based mark-recapture data from an intensively monitored polygamous population of snowy plovers. We show that a strongly male-biased ASR (0.63) is primarily driven by sex-specific survival of juveniles rather than adults or dependent offspring. This finding provides empirical support for theories of unbiased sex allocation when sex differences in survival arise after the period of parental investment. Importantly, a conventional model ignoring sex biases significantly overestimated population viability. We suggest that sex-specific population models are essential to understand the population dynamics of sexual organisms: reproduction and population growth are most sensitive to perturbations in survival of the limiting sex. Overall, our study suggests that sex-biased early survival may contribute toward mating system evolution and population persistence, with implications for both sexual selection theory and biodiversity conservation.
成体性别比例（ASR）是种群生物学中的一个核心概念，也是性选择的关键因素，但为什么大多数人口模型忽略性别偏差呢？生命关键期的死亡率在性别之间和整个生命史中经常存在差异，但它们对 ASR 变化的相对贡献仍知之甚少——这是评估野外性别比例理论和为保护提供信息的必要步骤。在这里，我们将两性结构的种群模型与来自一个经过密集监测的雪鹀多配偶种群的个体基础标记重捕数据相结合。我们表明，强烈的雄性偏性 ASR（0.63）主要是由幼体的性别特异性存活率驱动的，而不是由成体或依赖后代驱动的。这一发现为在父母投资期后出现的生存性别差异时的无偏性别分配理论提供了经验支持。重要的是，忽略性别偏差的传统模型显著高估了种群生存力。我们认为，两性人口模型对于理解有性生物的种群动态至关重要：繁殖和种群增长对限制性别存活率的干扰最为敏感。总的来说，我们的研究表明，早期生存的性别偏向可能有助于交配系统的进化和种群的维持，这对性选择理论和生物多样性保护都有影响。
