Data from: Population density and climate shape early-life survival and recruitment in a long-lived pelagic seabird

1. Our understanding of demographic processes is mainly based on analyses of traits from the adult component of populations. Early-life demographic traits are poorly known mainly for methodological reasons. Yet, survival of juvenile and immature individuals is critical for the recruitment into the population and thus for the whole population dynamic, especially for long-lived species. This bias currently restrains our ability to fully understand population dynamics of long-lived species and life-history theory. 2. The goal of this study was to estimate the early-life demographic parameters of a long-lived species with a long immature period (9–10 years), to test for sex and age effects on these parameters and to identify the environmental factors encountered during the period of immaturity that may influence survival and recruitment. 3. Using capture–mark–recapture multievent models allowing us to deal with uncertain and unobservable individual states, we analysed a long-term data set of wandering albatrosses to estimate both age- and sex-specific early-life survival and recruitment. We investigated environmental factors potentially driving these demographic traits using climatic and fisheries covariates and tested for density dependence. 4. Our study provides for the first time an estimate of annual survival during the first 2 years at sea for an albatross species (0·801 ± 0·014). Both age and sex affected early-life survival and recruitment processes of this long-lived seabird species. Early-life survival and recruitment were highly variable across years although the sensitivity of young birds to environmental variability decreased with age. Early-life survival was negatively associated with sea surface temperature, and recruitment rate was positively related to both Southern Annular Mode and sea surface temperature. We found strong evidence for density-dependent mortality of juveniles. Population size explained 41% of the variation of this parameter over the study period. 5. These results indicate that early-life survival and recruitment were strongly age and sex dependent in a dimorphic long-lived species. In addition, early-life demographic parameters were affected by natal environmental conditions and by environmental conditions faced during the period of immaturity. Finally, our results constitute one of the first demonstrations of density dependence on juvenile survival in seabirds, with major consequences for our understanding of population dynamics in seabirds.

1. 我们对种群动态过程的认知，主要依托于对种群成年个体性状的分析。早期生活史种群性状因方法学层面的限制，迄今仍少有详实研究。然而，幼体与未成熟个体的存活对于种群补充至关重要，进而关乎整个种群的动态变化，对长寿物种而言尤为如此。当前的这一认知偏差，制约了我们全面解析长寿物种种群动态与生活史理论的能力。
2. 本研究旨在估算一种未成熟阶段长达9~10年的长寿物种的早期生活史种群参数，检验性别与年龄对这些参数的影响，并识别未成熟阶段中可能影响存活与种群补充的环境因子。
3. 本研究采用可处理不确定与不可观测个体状态的捕获-标记-再捕获（capture–mark–recapture）多事件模型（multievent models），对漂泊信天翁（wandering albatrosses）的长期数据集展开分析，以估算分年龄与分性别的早期存活与种群补充情况。本研究借助气候与渔业协变量，探究了潜在驱动这些种群性状的环境因子，并检验了密度依赖效应。
4. 本研究首次估算了某信天翁物种在海上最初2年的年存活率（0.801 ± 0.014）。年龄与性别均会影响该长寿海鸟的早期存活与种群补充过程。尽管幼鸟对环境变异的敏感性随年龄增长而降低，但早期存活与种群补充在不同年份间存在极高的变异性。早期存活率与海表温度（Sea Surface Temperature）呈负相关，而种群补充率则与南半球环状模（Southern Annular Mode）及海表温度均呈正相关。本研究发现了幼体密度依赖型死亡率的有力证据：在整个研究周期内，种群大小解释了该参数41%的变异量。
5. 上述结果表明，在这种具有性别二态性的长寿物种中，早期存活与种群补充显著受年龄与性别调控。此外，早期生活史种群参数会受出生环境以及未成熟阶段所遭遇的环境条件影响。最后，本研究结果是海鸟幼体存活存在密度依赖效应的首批佐证之一，这对我们理解海鸟的种群动态具有重要意义。