Behavioral and physiological ecologists have long been interested in explaining the causes and consequences of trait variation, with a focus on individual differences in mean values. However, the majority of phenotypic variation typically occurs within individuals, rather than among individuals (as indicated by average repeatability being less than 0.5). Recent studies have further shown that individuals can also differ in the magnitude of variation that is unexplained by individual variation or environmental factors (i.e., residual variation). The significance of residual variation, or why individuals differ, is largely unexplained, but is important from evolutionary, methodological, and statistical perspectives. Here, we broadly reviewed literature on individual variation in behavior and physiology, and located 39 datasets with sufficient repeated measures to evaluate individual differences in residual variance. We then analyzed these datasets using methods that permit direct comparisons of parameters across studies. This revealed substantial and widespread individual differences in residual variance. The magnitude of individual variation appeared larger in behavioral traits than in physiological traits, and heterogeneity was greater in more controlled situations. We discuss potential ecological and evolutionary implications of individual differences in residual variance and suggest productive future research directions.

中文翻译：

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理解无法解释的：残差方差中个体差异的幅度和相关性

行为和生理生态学家长期以来一直对解释性状变异的原因和后果感兴趣，重点关注平均值的个体差异。然而，大多数表型变异通常发生在个体内部，而不是个体之间（如平均重复性小于 0.5 所示）。最近的研究进一步表明，个体也可能存在个体变异或环境因素无法解释的变异幅度（即残余变异）。残差的重要性，或者个体差异的原因，在很大程度上是无法解释的，但从进化、方法和统计的角度来看很重要。在这里，我们广泛回顾了有关行为和生理学个体差异的文献，并定位了 39 个具有足够重复测量的数据集，以评估残差方差的个体差异。然后，我们使用允许跨研究直接比较参数的方法分析这些数据集。这揭示了残差方差的实质性和广泛的个体差异。行为特征的个体变异幅度大于生理特征，并且在更可控的情况下异质性更大。我们讨论了残差方差中个体差异的潜在生态和进化影响，并提出了富有成效的未来研究方向。这揭示了残差方差的实质性和广泛的个体差异。行为特征的个体变异幅度大于生理特征，并且在更可控的情况下异质性更大。我们讨论了残差方差中个体差异的潜在生态和进化影响，并提出了富有成效的未来研究方向。这揭示了残差方差的实质性和广泛的个体差异。行为特征的个体变异幅度大于生理特征，并且在更可控的情况下异质性更大。我们讨论了残差方差中个体差异的潜在生态和进化影响，并提出了富有成效的未来研究方向。