Data from: Luck or pluck: does trait variation or chance drive variation in lifetime reproductive success?

While there has been extensive interest in how intraspecific trait variation affects ecological processes,
outcomes are highly variable even when individuals are identical: some are
lucky while others are not. Trait variation is therefore only important if it adds substantially to the
variability produced by luck. We ask when trait variation has a substantial effect on variability in
lifetime reproductive success (LRS), using two approaches: 1) we partition the variation in LRS into
contributions from luck and trait variation; 2) we ask what can be inferred about an individual's
traits, and with what certainty, given their observed LRS. In theoretical stage- and size-structured models,
and two empirical case studies, we find that luck usually dominates the variance of LRS. Even when individuals
differ substantially in ways that affect expected LRS, unless the effects of luck are substantially
reduced (e.g. low variability in reproductive lifespan or in annual fecundity), most variance in
lifetime outcomes is due to luck, implying that departures from "null" models omitting trait
variation will be hard to detect. Luck also obscures the relationship between realized LRS
and individual traits. While trait variation may influence the fate of populations, luck
often governs the lives of individuals.

尽管学界已就种内性状变异（intraspecific trait variation）对生态过程的影响展开了广泛研究，但即便个体的固有性状完全一致，其繁殖结果仍存在高度异质性——部分个体更为“幸运”，其余个体则不然。因此，种内性状变异仅当其显著增加由随机机遇所产生的变异幅度时，才具备实际研究意义。本研究通过两种研究路径，探讨种内性状变异何时会对终生繁殖成功率（lifetime reproductive success, LRS）的变异产生显著影响：其一，将LRS的变异拆解为随机机遇与性状变异的贡献分量；其二，在已知个体观测到的LRS的前提下，探究可如何推断其性状特征，以及该推断的确定性程度。在理论阶段-体型结构化模型，以及两项实证案例研究中，我们发现随机机遇通常主导了LRS的变异。即便个体间存在诸多显著影响其预期LRS的性状差异，除非随机机遇的影响被大幅削弱（例如繁殖寿命或年度繁殖力的变异程度较低），绝大多数终生繁殖结果的变异仍源于随机机遇。这意味着，省略性状变异的“零模型”（null model）的偏差将难以被检测到。随机机遇还会掩盖实际观测到的LRS与个体性状间的关联。尽管性状变异或许会影响种群的存续命运，但随机机遇往往主导着个体的生存与繁殖历程。