Data from: Individual quality and age but not environmental or social conditions modulate costs of reproduction in a capital breeder

Costs associated with reproduction are widely known to play a role in the evolution of reproductive tactics with consequences to population and eco-evolutionary dynamics. Evaluating these costs as they pertain to species in the wild remains an important goal of evolutionary ecology. Individual heterogeneity, including differences in individual quality (i.e., among-individual differences in traits associated with survival and reproduction) or state, and variation in environmental and social conditions can modulate the costs of reproduction; however, few studies have considered effects of these factors simultaneously. Taking advantage of a detailed, long-term dataset for a population of feral horses (Sable Island, Nova-Scotia, Canada), we address the question of how intrinsic (quality, age), environmental (winter severity, location), and social conditions (group size, composition, sex ratio, density) influence the costs of reproduction on subsequent reproduction. Individual quality was measured using a multivariate analysis on a combination of four static and dynamic traits expected to depict heterogeneity in individual performance. Female quality and age interacted with reproductive status of the previous year to determine current reproductive effort, while no effect of social or environmental covariates was found. High quality females showed higher probabilities of giving birth and weaning their foal regardless of their reproductive status the previous year, while those of lower quality showed lower probabilities of producing foals in successive years. Middle-aged (prime) females had the highest probability of giving birth when they had not reproduced the year before but no such relationship with age was found among females that had reproduced the previous year, indicating that prime-aged females bear higher costs of reproduction. We show that individual quality and age were key factors modulating the costs of reproduction in a capital breeder but that environmental or social conditions were not, highlighting the importance of considering multiple factors when studying costs of reproduction.繁殖相关成本在繁殖策略的演化过程中发挥着关键作用，其效应可波及种群动态与生态演化动力学，这一结论已得到学界广泛认可。 针对野生物种评估此类繁殖成本，仍是进化生态学领域的重要研究目标。 个体异质性——包括个体质量（individual quality，即与存活和繁殖相关的性状在个体间的差异）或个体状态的差异，以及环境与社会条件的变异——均可对繁殖成本产生调控作用；但目前鲜有研究同时考量这些因素的综合影响。 本研究依托加拿大新斯科舍省萨布尔岛（Sable Island）野生马种群的长期详细数据集，旨在探究内在因素（个体质量、年龄）、环境因素（冬季严酷程度、栖息位置）以及社会条件（群体规模、群体组成、性比、种群密度）如何影响繁殖成本对后续繁殖的作用。 研究通过对四项静态与动态性状的组合开展多变量分析，以此量化个体质量，这些性状可反映个体表现的异质性。 雌性个体质量与年龄，会与上一年的繁殖状态产生交互作用，共同决定当前的繁殖投入；而本研究未发现社会或环境协变量存在显著效应。 无论上一年是否参与繁殖，高质量雌性的产驹概率与断奶成功率均更高；而低质量雌性在连续年份中产驹的概率则相对更低。 未在去年繁殖的中年（繁殖盛期）雌性，产驹概率最高；但去年已繁殖的雌性中，未观察到年龄与产驹概率存在此类关联，这表明繁殖盛期雌性承担的繁殖成本更高。 本研究证实，在资本繁育者（capital breeder）中，个体质量与年龄是调控繁殖成本的核心因素，而环境与社会条件并非如此，这一结果凸显了在繁殖成本研究中综合考量多因素的重要性。