Data from: Mating success and body condition not related to foraging specializations in male fur seals

Individual specialization is widespread among wild populations. While its fitness consequences are central in predicting the ecological and evolutionary trajectories of populations, they remain poorly understood. Long-term individual foraging specializations occur in male Antarctic (Arctocephalus gazella) and Australian (A. pusillus doriferus) fur seals. Strong selective pressure is expected in these highly dimorphic and polygynous species, raising the question of the fitness payoffs associated with different foraging strategies. We investigated the relationship between individual isotopic niche (a proxy of foraging specialization), body size and condition, and an index of reproductive success (harem size) in territorial males. Individuals varied greatly in their skin and fur isotopic values reflecting a range of foraging strategies within the two populations. However, in both species, isotopic niche was not correlated to body size, condition or mating success (R2/ρ < 0.06). Furthermore, no foraging niche was predominant in either species, which would have indicated a substantial long-term fitness benefit of a particular strategy via a higher survival rate. These results suggest that the fitness consequences of a foraging strategy depend not only on the quality of prey and feeding habitat but also on an individual's hunting efficiency and skills.

野生种群中普遍存在个体特化现象。尽管其适合度后果是预测种群生态与进化轨迹的核心要素，但目前对其仍知之甚少。南极海狗（Arctocephalus gazella）与澳大利亚海狗（A. pusillus doriferus）的雄性个体均存在长期的觅食特化现象。这两类物种具有高度的性别二态性且为多配性，预期存在较强的选择压力，由此引出了不同觅食策略对应的适合度收益这一研究问题。我们针对领地雄性个体，探究了个体同位素生态位（isotopic niche，作为觅食特化的替代指标）、体型与身体状况，以及繁殖成功指标（配偶群规模）之间的关联。两个种群的个体在皮肤和被毛的同位素值上差异显著，反映出其觅食策略的多样性。然而在两个物种中，同位素生态位均与体型、身体状况或交配成功率无显著关联（决定系数R²/秩相关系数ρ < 0.06）。此外，两个物种中均未出现占主导地位的觅食生态位——这原本可以表明某一特定策略可通过更高的存活率带来显著的长期适合度收益。这些结果表明，觅食策略的适合度后果不仅取决于猎物与觅食生境的质量，还与个体的捕猎效率及技能水平相关。