Data from: Tracking restoration of population diversity via the portfolio effect

1. Declines in diversity among populations managed together have diminished aggregate stability through a decreased portfolio effect. Although the portfolio effect has been quantified in a variety of ways, management recommendations for the recovery of lost diversity rarely specify the stability benefits possible through such improvements. 2. We introduce a metric, the Diversity Deficit (<i>DD</i>), that relates past losses and potential gains in aggregate stability to the changes in population diversity (i.e., covariability among population time series). We illustrate use of this <i>DD</i> in retrospective analyses of the aggregate Sacramento River Fall-run Chinook salmon stock (<i>Oncorhynchus tshawytscha</i>), and project potential future improvements in stability through population diversity. 3. In the retrospective analysis, we removed individual time series from the stability calculations to determine their effects on times and locations of past losses in diversity and stability. We found an early threefold loss in stock stability resulting from the presence of a single tributary, the Sacramento River mainstem. Other shifts in stability resulted from an increase in variability of a single population, and from the synchronizing effects of low ocean survival that led to the 2008-09 fishery closure. Only one, smaller increase in the <i>DD</i> (i.e., in lost stability) was due to portfolio-wide increases in covariabilities among tributary abundances. 4. In a prospective analysis using the <i>DD</i> applied to California salmon, we found that increasing biodiversity to the point of population independence and to its early high value would have reduced the probability of triggering a fishery closure. 5. Synthesis and applications. Analyses with the <i>DD</i> illustrate a means to identify the times and locations of losses in population diversity, and to quantify how much restoration of population diversity could increase stability, thus benefit resource services. Here the benefit was a reduction in the probability of falling below a critical management threshold leading to fishery closure, but other tangible benefits (e.g., reduction in probability of extinction) would be possible.12-Jun-2017

1. 协同管理种群的多样性下降通过削弱投资组合效应（portfolio effect）降低了整体稳定性。尽管已有多种方法对投资组合效应进行量化，但针对受损多样性恢复的管理建议，极少明确提及通过此类多样性提升所能获得的稳定性增益。
2. 本研究提出一项名为多样性赤字（Diversity Deficit，DD）的指标，该指标将整体稳定性的既往损失与潜在增益，与种群多样性的变化（即种群时间序列间的协变关系）关联起来。我们以萨克拉门托河秋季洄游奇努克鲑鱼（*Oncorhynchus tshawytscha*）整体种群的回溯性分析为例，展示了该DD指标的应用，并预测了通过种群多样性提升可实现的未来稳定性增益。
3. 在回溯性分析中，我们通过从稳定性计算中移除单一条时间序列，以明确其对既往多样性与稳定性损失的发生时间与地点的影响。研究发现，萨克拉门托河干流这单一支流的存在，早在早期便导致种群稳定性出现三倍下降。其余稳定性变化则源于单一种群变异性的提升，以及导致2008-2009年渔业休渔的海洋存活率偏低所引发的同步效应。仅存在一次规模较小的DD上升（即稳定性损失加剧），其成因是各支流种群丰度间的协变程度在整体组合范围内提升。
4. 在针对加州鲑鱼的DD前瞻性分析中，我们发现，若将生物多样性提升至种群相互独立的水平，并恢复至早期的高值状态，可降低触发渔业休渔的概率。
5. 综合与应用。基于DD的分析提供了一套可行方法，可精准识别种群多样性损失的发生时间与空间位置，并量化种群多样性修复所能带来的稳定性提升幅度，进而为资源服务创造收益。本研究中的收益体现为降低了跌破关键管理阈值并引发渔业休渔的概率，但诸如降低灭绝概率等其他有形收益同样具备实现可能。
2017年6月12日