Data from: Reproductive success is energetically linked to foraging efficiency in Antarctic fur seals

The efficiency with which individuals extract energy from their environment defines their survival and reproductive success, and thus their selective contribution to the population. Individuals that forage more efficiently (i.e., when energy gained exceeds energy expended) are likely to be more successful at raising viable offspring than individuals that forage less efficiently. Our goal was to test this prediction in large long-lived mammals under free-ranging conditions. To do so, we equipped 20 lactating Antarctic fur seals (Arctocephalus gazella) breeding on the Kerguelen Island in the Southern Ocean with tags that recorded GPS locations, depth and tri-axial acceleration to determine at-sea behaviours and detailed time-activity budgets during their foraging trips. We also simultaneously measured energy spent at sea using the doubly-labeled water (DLW) method, and estimated the energy acquired while foraging from 1) type and energy content of prey species present in scat remains, and 2) numbers of prey capture attempts determined from head acceleration. Finally, we followed the growth of 36 pups from birth until weaning (of which 20 were the offspring of our 20 tracked mothers), and used the relative differences in body mass of pups at weaning as an index of first year survival and thus the reproductive success of their mothers. Our results show that females with greater foraging efficiencies produced relatively bigger pups at weaning. These mothers achieved greater foraging efficiency by extracting more energy per minute of diving rather than by reducing energy expenditure. This strategy also resulted in the females spending less time diving and less time overall at sea, which allowed them to deliver higher quality milk to their pups, or allowed their pups to suckle more frequently, or both. The linkage we demonstrate between reproductive success and the quality of individuals as foragers provides an individual-based quantitative framework to investigate how changes in the availability and accessibility of prey can affect fitness of animals.

个体从环境中获取能量的效率，决定了其生存与繁殖成功率，进而决定其对种群的选择性贡献。觅食效率更高的个体（即获取的能量多于消耗的能量），相比觅食效率较低的个体，更有可能成功抚育出可存活的后代。本研究旨在自由活动的野生大型长寿哺乳动物中验证这一预测。为此，我们为南大洋凯尔盖朗岛上繁殖的20头泌乳期南极海狗（Antarctic fur seal, Arctocephalus gazella）佩戴了记录GPS位置、水深及三轴加速度（tri-axial acceleration）的标签，以确定其海上行为及觅食旅途中的详细时间-活动预算（time-activity budgets）。我们还通过双标记水法（doubly-labeled water, DLW）同步测定了它们在海上的能量消耗，并从两方面估算觅食过程中获取的能量：1）粪便残骸中发现的猎物种类及其能量含量；2）通过头部加速度数据确定的猎物捕获尝试次数。最后，我们追踪了36头海狗幼崽从出生到断奶的生长过程（其中20头为本次研究追踪的20头母海狗的后代），并将断奶时幼崽的体质量相对差异作为幼崽第一年存活率的指标，进而反映其母海狗的繁殖成功率。研究结果显示，觅食效率更高的母海狗，其幼崽在断奶时的体质量相对更大。这类母海狗通过提升每分钟潜水的能量获取量，而非降低能量消耗，来实现更高的觅食效率。这种策略还使母海狗的潜水时长与海上总停留时长更短，从而能够为幼崽提供更高质量的乳汁，或让幼崽获得更频繁的哺乳，或两者兼具。本研究揭示的繁殖成功率与个体觅食能力之间的关联，为探讨猎物可获得性与可获取性变化如何影响动物的进化适合度提供了基于个体的量化框架。