The cost of reproduction: differential resource specialization in female and male California sea otters
The cost of reproduction: differential resource specialization in female and male California sea otters
复制标题
繁殖成本：雌性和雄性加州海獭的资源专业化差异
作者：
Emma A. Elliott Smith;S. Newsome;J. Estes;M. Tinker
行为和饮食的种内差异可能会对种群和生态系统动态产生重要影响。在这里，我们研究了生殖投资和空间生态的差异如何影响雄性和雌性南方海獭(Enhya Lutris Nereis)的个体饮食专业化。我们假设，更大的生殖限制和更小的雌性范围导致更明显的种内竞争和更高的专门化。我们将稳定碳(δ13C)和氮(δ15N)的同位素分析与对加州五个亚群的长期观察研究结合在一起。我们将个体饮食专业化定义为个体内变异(WIC)与总种群生态位宽度(TNW)的低比率。我们使用一般的线性和线性混合效应模型，将男性和女性的WIC/TNW的同位素和观测指标与人口密度和运动模式的数据进行比较。与我们的假设一致，人口密度的增加与女性个体饮食专业化程度的提高有关，而与男性的个体饮食专业化程度无关。此外，我们发现，海獭栖息地的海岸线数量与个体的食物变异性呈正相关，范围跨度的增加导致雄性和雌性的专业性都较弱。我们将我们的结果归因于基于性别的运动差异，雌性需要专攻它们的小范围以最大化能量获取，并假设种内竞争增加的海獭个体猎物专门化的范例可能主要是由雌性驱动的模式。我们的工作突显了性别在促进和维持饮食专业化的机械性压力中可能发挥的更广泛的作用。
Intraspecific variation in behavior and diet can have important consequences for population and ecosystem dynamics. Here, we examine how differences in reproductive investment and spatial ecology influence individual diet specialization in male and female southern sea otters (Enhydra lutris nereis). We hypothesize that greater reproductive constraints and smaller home ranges of females lead to more pronounced intraspecific competition and increased specialization. We integrate stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of sea otter vibrissae with long-term observational studies of five subpopulations in California. We define individual diet specialization as low ratios of within-individual variation (WIC) to total population niche width (TNW). We compare isotopic and observational based metrics of WIC/TNW for males and females to data on population densities, and movement patterns using both general linear and linear mixed-effects models. Consistent with our hypothesis, increasing population density is associated with increased individual diet specialization by females but not by males. Additionally, we find the amount of coastline in a sea otter’s home range positively related with individual dietary variability, with increased range span resulting in weaker specialization for both males and females. We attribute our results to sex-based differences in movement, with females needing to specialize in their small ranges to maximize energy gain, and posit that the paradigm of individual prey specialization in sea otters with increased intraspecific competition may be a pattern driven largely by females. Our work highlights a potentially broader role of sex in the mechanistic pressures promoting and maintaining diet specialization.