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.

尽管学界已对种内性状变异（intraspecific trait variation）如何影响生态过程产生了广泛研究兴趣，但即便所有个体完全一致，其生态结果仍存在高度异质性：部分个体因随机机遇获益，其余则反之。因此，种内性状变异仅当其能显著放大由随机机遇所导致的变异时，才具备实际研究意义。本研究采用两种方法，探讨种内性状变异何时会对终身繁殖成功率（lifetime reproductive success, LRS）的变异产生显著影响：其一，将LRS的变异分解为随机机遇与性状变异的贡献份额；其二，基于观测到的个体LRS，探究可推断出哪些个体性状，以及该推断的置信度如何。在基于阶段与体型结构构建的理论模型，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的变异量。即便个体在影响预期LRS的性状上存在显著差异，除非随机机遇的影响被大幅削弱（例如繁殖寿命或年繁殖力的变异程度较低），否则终身繁殖结果的绝大多数变异仍源自随机机遇。这意味着，省略性状变异的"null"模型所产生的偏差，往往难以被检测到。此外，随机机遇还会掩盖实际观测到的LRS与个体性状之间的关联。尽管性状变异可能会影响种群的存续命运，但随机机遇往往决定了单个个体的生存与繁殖结局。