Individual heterogeneity is variation in trait expression observed among individuals of a population. Individual heterogeneity in the pre‐breeder stage of development is of importance given its eventual contribution to the breeding population's overall reproductive performance. Yet most studies do not consider the role of individual heterogeneity in pre‐breeders when investigating population processes. We investigated individual heterogeneity in the survival and recruitment probabilities of pre‐breeding male southern elephant seals Mirounga leonina using 34 years of data collected at Marion Island. Elephant seals are highly polygynous capital breeders, with few male offspring surviving to compete in breeding events and even fewer breeding successfully. Specifically, we fitted finite‐mixture models with two hidden groups that represented ‘robust’ and ‘frail’ individuals and compared the demographic rates of these groups to that of the population. Survival and recruitment as first‐time subordinate breeders could be distinguished between groups. Survival of both robust and frail pre‐breeders decreased from age 2, whilst differences between groups were maintained (ontogeny processes). Frail pre‐breeders had a much lower survival than the population average, suggesting that frail individuals were preferentially removed from the population (selective disappearance). Differences in recruitment probabilities were apparent from age 5 (earliest recorded age) and increased until age 7, with most recruits comprising robust pre‐breeders. Male pre‐breeders were more likely to be robust at age 2 when born in years with few conspecifics, suggesting that individual heterogeneity was determined, in part, by density‐dependent effects. A population projection model revealed that male breeders of every age class never consisted of more than 5% of frail recruits. Rather, the breeding population increasingly consisted of robust recruits that obtained social dominance with age. We demonstrated that individual heterogeneity in male pre‐breeder demographic rates was present and persistent throughout much of development and determined the proportion of adult males that obtained social dominance.

中文翻译：

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脆弱少年的选择性失踪：了解成年雄象海豹社会优势的后果

个体异质性是在种群个体之间观察到的性状表达变异。繁殖前期阶段的个体异质性很重要，因为它最终会影响育种种群的总体繁殖性能。但是，大多数研究在调查种群过程时都没有考虑个体异质性在繁育者中的作用。我们调查了雄性南部象海豹Mirounga leonina的繁殖和繁殖概率中的个体异质性使用在马里恩岛（Marion Island）收集的34年数据。象海豹是高度多性的资本繁殖者，存活下来参加竞争繁殖活动的雄性后代很少，成功繁殖的甚至更少。具体来说，我们将有限混合模型与代表“健壮”和“脆弱”个体的两个隐藏群体进行拟合，并将这些群体的人口比率与人口比率进行比较。可以区分不同群体的首次成年育种者的生存和招募。从2岁开始，健壮和脆弱的种羊的存活率都下降了，而群体之间的差异得以维持（个体发育过程）。体弱的种犬的存活率远低于人口平均水平，这表明体弱的个体优先从种群中移出（选择性失踪）。从5岁（最早记录的年龄）开始，招聘概率的差异就很明显，直到7岁时才有所增加，大多数招聘者都拥有强大的前育种者。男性预育者出生在几岁而没有特定物种的情况下，更容易在2岁时变得健壮，这表明个体异质性部分取决于密度依赖性效应。人口预测模型显示，各个年龄段的雄性育种人员中，体弱者的比例均不超过5％。相反，育种种群越来越多地由随着年龄增长而获得社会支配地位的强大新兵组成。我们证明了男性在育种前的人口统计学上的异质性在整个发展过程中都存在并持续存在，并确定了获得社会支配地位的成年男性的比例。