Data from: Spatial variation buffers temporal fluctuations in early juvenile survival for an endangered Pacific salmon

1. Spatial, phenotypic, and genetic diversity at relatively small scales can buffer species against large-scale processes such as climate change that tend to synchronize populations and increase temporal variability in overall abundance or production. This portfolio effect generally results in improved biological and economic outcomes for managed species. Previous evidence for the portfolio effect in salmonids has arisen from examinations of time series of adult abundance, but we lack evidence of spatial buffering of temporal variability in demographic rates such as survival of juveniles during their first year of life. 2. We therefore use density-dependent population models with multiple random effects to represent synchronous (similar among populations) and asynchronous (different among populations) temporal variability as well as spatial variability in survival. These are fitted to 25 years of survey data for breeding adults and surviving juveniles from 15 demographically distinct populations of Chinook salmon (Oncorhynchus tshawytscha) within a single metapopulation in the Snake River in Idaho, USA. 3. Model selection identifies the most support for the model that included both synchronous and asynchronous temporal variability, in addition to spatial variability. Asynchronous variability (log-SD = 0.55) is approximately equal in magnitude to synchronous temporal variability (log-SD = 0.67), but much lower than spatial variability (log-SD = 1.11). We also show that the pairwise correlation coefficient, a common measure of population synchrony, is approximated by the estimated ratio of shared and total variance, where both approaches yield a synchrony estimate of 0.59. We therefore find evidence for spatial buffering of temporal variability in early juvenile survival, although between-population variability that persists over time is also large. 4. We conclude that spatial variability decreases interannual changes in overall juvenile production, which suggests that conservation and restoration of spatial diversity will improve population persistence for this metapopulation. However, the exact magnitude of spatial buffering depends upon demographic parameters such as adult survival that may vary among populations, and is proposed as an area of future research using hierarchical life cycle models. We recommend that future sampling of this metapopulation employ a repeated-measure sampling design to improve estimation of early juvenile carrying capacity.

1. 较小尺度下的空间、表型与遗传多样性，可使物种种群获得抵御气候变化等大尺度过程的缓冲能力——这类大尺度过程往往会同步种群动态，并加剧种群总丰度或总生产力的时间变异性。该投资组合效应（portfolio effect）通常可提升管护物种的生物学与经济学效益。此前关于鲑科鱼类（salmonids）投资组合效应的研究证据，均基于对成体丰度时间序列的分析，但目前仍缺乏针对种群统计率（如幼体第一年存活率）的时间变异性所存在的空间缓冲效应的相关证据。
2. 为此，我们构建包含多重随机效应的密度依赖种群模型，用以刻画同步性（种群间特征相似）与异步性（种群间特征相异）的时间变异性，以及存活过程中的空间变异性。我们将该模型拟合至美国爱达荷州斯内克河某一集合种群（metapopulation）内15个种群统计特征独立的奇努克鲑（Chinook salmon, *Oncorhynchus tshawytscha*）的25年调查数据，数据涵盖繁殖成体与存活幼体的相关信息。
3. 模型选择结果显示，同时纳入同步性与异步性时间变异性、外加空间变异性的模型获得最多支持。异步变异性（对数标准差=0.55）的量级与同步性时间变异性（对数标准差=0.67）大致相当，但远低于空间变异性（对数标准差=1.11）。我们还发现，衡量种群同步性的常用指标——两两相关系数，可通过共享方差与总方差的估计比值近似得到，两种方法均得到0.59的同步性估计值。因此，我们找到了幼体早期存活的时间变异性存在空间缓冲效应的证据，尽管种群间持续存在的时间变异性仍较为显著。
4. 本研究表明，空间变异性可降低幼体总生产力的年际变化，这意味着保护与恢复空间多样性，将提升该集合种群的存续能力。不过，空间缓冲的具体幅度取决于种群间存在差异的种群统计参数（如成体存活率），未来可采用层级生命周期模型对此展开研究。我们建议，未来对该集合种群的采样应采用重复测量采样设计，以优化幼体早期承载量的估计精度。