Foraging Fidelity as a Recipe for a Long Life: Foraging Strategy and Longevity in Male Southern Elephant Seals

Identifying individual factors affecting life-span has long been of interest for biologists and demographers: how do some individuals manage to dodge the forces of mortality when the vast majority does not? Answering this question is not straightforward, partly because of the arduous task of accurately estimating longevity in wild animals, and of the statistical difficulties in correlating time-varying ecological covariables with a single number (time-to-event). Here we investigated the relationship between foraging strategy and life-span in an elusive and large marine predator: the Southern Elephant Seal (Mirounga leonina). Using teeth recovered from dead males on îles Kerguelen, Southern Ocean, we first aged specimens. Then we used stable isotopic measurements of carbon () in dentin to study the effect of foraging location on individual life-span. Using a joint change-point/survival modelling approach which enabled us to describe the ontogenetic trajectory of foraging, we unveiled how a stable foraging strategy developed early in life positively covaried with longevity in male Southern Elephant Seals. Coupled with an appropriate statistical analysis, stable isotopes have the potential to tackle ecological questions of long standing interest but whose answer has been hampered by logistic constraints.长期以来，识别影响寿命的个体层面因素始终是生物学家与人口统计学家的研究热点：为何绝大多数个体难以逃脱死亡的宿命，却有部分个体得以幸免？解答这一问题并非易事，究其原因，一方面是准确估算野生动物寿命的任务颇为艰巨，另一方面则是将随时间变化的生态协变量与单一数值（事件发生时间（time-to-event））进行关联时存在统计学难点。本研究针对一种行踪隐秘的大型海洋掠食者——南象海豹（Mirounga leonina），探讨了其觅食策略与寿命之间的关联。研究团队从南大洋凯尔盖朗群岛（îles Kerguelen）的死亡雄性南象海豹身上获取牙齿样本，首先对个体进行了年龄鉴定。随后通过测定牙本质中的碳（carbon）稳定同位素比值，探究了觅食区位对个体寿命的影响。本研究采用变点-生存联合建模方法，得以刻画觅食行为的个体发育轨迹，进而揭示了雄性南象海豹在生命早期形成的稳定觅食策略如何与更长寿命呈现正相关关系。结合恰当的统计学分析手段，稳定同位素技术有望解决那些长期以来备受学界关注、却因后勤限制难以获得答案的生态学问题。