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。尽管个体特化的适合度（fitness）效应是预测种群生态与进化动态轨迹的核心变量，但目前学界对其认知仍较为匮乏。雄性南极海狗（Arctocephalus gazella）与澳洲海狗（A. pusillus doriferus）种群中，存在长期稳定的个体觅食特化行为。这类雌雄高度二型且实行一雄多雌制的物种面临较强的选择压力，由此引出了不同觅食策略对应的适合度收益这一核心科学问题。本研究以领域雄性个体为研究对象，探究了个体同位素生态位（isotopic niche，作为觅食特化的替代指标）、身体大小与身体状况，以及繁殖成功指标（后宫群大小，harem size）之间的关联。两个种群内的个体皮肤与被毛的同位素数值存在显著差异，反映出种群内存在多样化的觅食策略。然而，在两个物种中，同位素生态位均与身体大小、身体状况或交配成功率无显著相关（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；若存在占优觅食生态位，则意味着特定觅食策略可通过更高的存活率，带来显著的长期适合度收益。上述研究结果表明，觅食策略的适合度效应不仅取决于猎物资源与觅食生境的质量，还与个体自身的捕猎效率与技能水平密切相关。