Data from: We happy few: using structured population models to identify the decisive events in the lives of exceptional individuals

In any population, some individuals make it big: they are among the few that produce many offspring, grow to large size, and so on. What distinguishes the lives of these happy few? We present three approaches for identifying what factors distinguish those “lucky” individuals who come to dominate reproduction in a population without fixed differences between individuals (genotype, site quality, etc.): comparing life-history trajectories for lucky and unlucky individuals and calculating the elasticity of the probability of becoming lucky to perturbations in demographic rates at a given size or a given age. As examples we consider published size-structured integral projection models for the tropical tree Dacrydium elatum and the semiarid shrub Artemisia ordosica and an age-size-structured matrix model for the tropical tree Cedrela ordosica. We find that good fortune (e.g., rapid growth) when small and young matters much more than good fortune when older and larger. Becoming lucky is primarily a matter of surviving while others die. For species with more variable growth (such as Cedrela and Ordosica), it is also a matter of growing fast. We focus on reproductive skew, but our methods are broadly applicable and can be used to investigate how individuals come to be exceptional in any aspect.

在任何种群中，总有部分个体能够脱颖而出：它们属于少数能产生大量后代、长成庞大体型的个体之列。这些少数成功个体的人生有何独特之处？我们提出了三种方法，用以甄别在个体间不存在固定差异（如基因型、生境质量等）的种群中，那些最终主导繁殖的"幸运"个体的区分因素：一是对比幸运个体与非幸运个体的生活史轨迹（life-history trajectories），二是计算在特定体型下，个体成为"幸运"个体的概率对种群统计率（demographic rates）扰动的弹性，三是计算在特定年龄下该概率对种群统计率扰动的弹性。作为示例，我们采用了已发表的三类模型：针对热带乔木鸡毛松（Dacrydium elatum）与半干旱灌木黑沙蒿（Artemisia ordosica）的体型结构积分投影模型（integral projection model, IPM），以及针对热带乔木Cedrela ordosica的年龄-体型结构矩阵模型。研究发现，个体在体型幼小、年龄较轻时的"好运"（如快速生长），远较其在年长体大时的好运更为关键；成为"幸运"个体的核心要素是在其他个体死亡时自身得以存活。对于生长变异程度更高的物种（如Cedrela ordosica与黑沙蒿），快速生长同样是关键因素。本研究聚焦于繁殖偏斜（reproductive skew）现象，但所提出的方法具有广泛适用性，可用于探究个体在任意维度上脱颖而出的成因。