Data from: Individual niche trajectories drive fitness variation

1. Variation in fitness across individuals is central to population growth, species coexistence, and evolution by natural selection. Fitness variation associated with resource use is hugely consequential, but how this variation is generated and maintained within natural populations remains unclear. In particular, individual fitness may depend on many cumulative foraging decisions over time, but this hypothesis remains untested. 2. We used multi-tissue stable isotope analysis to determine isotopic niche trajectories within species, populations and sexes of thin-toed frogs, and explored how this temporal dimension of diet affects individual reproductive investment, body condition, and parasite load. 3. We found that individual frogs shifted their diets less than expected under a null model, likely due to functional tradeoffs that limit the incorporation of new prey types over time. However, within the observed range of diet shifts, individuals that modified their diet to a greater degree exhibited higher fitness, although this effect was sex-dependent. 4. We suggest that these different relationships between isotopic niche trajectory length and fitness within thin-toed frogs are driven by variability in the resource environment, negative density-dependence and allometric constraints. These strong fitness effects suggest that the temporal dimension of diet change is a potential target of natural selection and, therefore, could drive correlated evolution in phenotypic traits underlying diet flexibility. Our findings add a new level of complexity to the understanding of ecological and evolutionary consequences of niche variation by demonstrating that temporal variation in foraging consistency within populations leads to different fitness payoffs.

1. 个体间适合度（fitness）的差异是种群增长、物种共存与自然选择下演化的核心要素。与资源利用相关的适合度变异影响深远，但这类变异在自然种群中如何产生并维持，目前仍不明晰。具体而言，个体适合度可能取决于随时间推移累积的多项觅食决策，但该假说尚未得到实证检验。
2. 我们采用多组织稳定同位素分析（multi-tissue stable isotope analysis），测定了细趾蟾不同物种、种群以及不同性别的同位素生态位轨迹（isotopic niche trajectories），并探讨了食谱的时间维度如何影响个体繁殖投入、身体状况与寄生虫负荷（parasite load）。
3. 本研究观测到，细趾蟾个体的食谱转变幅度低于零模型（null model）的预期值，这可能源于随时间推移限制新猎物类型摄入的功能权衡（functional tradeoffs）。不过在观测到的食谱转变范围内，食谱调整幅度更大的个体拥有更高的适合度，不过该效应存在性别依赖性。
4. 我们提出，细趾蟾种群内同位素生态位轨迹长度与适合度间的这类差异化关联，由资源环境变异性、负密度依赖（negative density-dependence）效应与异速生长限制（allometric constraints）共同驱动。这类显著的适合度效应表明，食谱变化的时间维度可能是自然选择的潜在作用靶点，因此能够推动与饮食灵活性相关的表型性状（phenotypic traits）的协同演化。本研究通过证实种群内觅食一致性的时间变异会带来差异化的适合度收益（fitness payoffs），为理解生态位变异的生态与演化后果增添了新的复杂维度。