Abstract：
Quantifying the variability in the delivery of ecosystem services across the landscape can be used to set appropriate management targets, evaluate resilience and target conservation efforts. Ecosystem functions and services may exhibit portfolio-type dynamics, whereby diversity within lower levels promotes stability at more aggregated levels. Portfolio theory provides a framework to characterize the relative performance among ecosystems and the processes that drive differences in performance. We assessed Pacific salmon Oncorhynchus spp. portfolio performance across their native latitudinal range focusing on the reliability of salmon returns as a metric with which to assess the function of salmon ecosystems and their services to humans. We used the Sharpe ratio (e.g. the size of the total salmon return to the portfolio relative to its variability (risk)) to evaluate the performance of Chinook and sockeye salmon portfolios across the west coast of North America. We evaluated the effects on portfolio performance from the variance of and covariance among salmon returns within each portfolio, and the association between portfolio performance and watershed attributes. We found a positive latitudinal trend in the risk-adjusted performance of Chinook and sockeye salmon portfolios that also correlated negatively with anthropogenic impact on watersheds (e.g. dams and land-use change). High-latitude Chinook salmon portfolios were on average 2·5 times more reliable, and their portfolio risk was mainly due to low variance in the individual assets. Sockeye salmon portfolios were also more reliable at higher latitudes, but sources of risk varied among the highest performing portfolios. Synthesis and applications. Portfolio theory provides a straightforward method for characterizing the resilience of salmon ecosystems and their services. Natural variability in portfolio performance among undeveloped watersheds provides a benchmark for restoration efforts. Locally and regionally, assessing the sources of portfolio risk can guide actions to maintain existing resilience (protect habitat and disturbance regimes that maintain response diversity; employ harvest strategies sensitive to different portfolio components) or improve restoration activities. Improving our understanding of portfolio reliability may allow for management of natural resources that is robust to ongoing environmental change. Portfolio theory provides a straightforward method for characterizing the resilience of salmon ecosystems and their services. Natural variability in portfolio performance among undeveloped watersheds provides a benchmark for restoration efforts. Locally and regionally, assessing the sources of portfolio risk can guide actions to maintain existing resilience (protect habitat and disturbance regimes that maintain response diversity; employ harvest strategies sensitive to different portfolio components) or improve restoration activities. Improving our understanding of portfolio reliability may allow for management of natural resources that is robust to ongoing environmental change.
摘要：
量化整个景观中生态系统服务交付的可变性可用于设定适当的管理目标，评估复原力和目标保护工作。生态系统功能和服务可能表现出投资组合型动态，因此，较低水平的多样性促进了更多聚集水平的稳定性。投资组合理论提供了一个框架来描述生态系统之间的相对绩效以及驱动绩效差异的过程。我们评估了太平洋鲑鱼Oncorhynchusspp。投资组合在其本地纬度范围内的表现，专注于鲑鱼回报的可靠性，作为评估鲑鱼生态系统功能及其对人类服务的指标。我们使用夏普比率（例如，投资组合的鲑鱼总收益相对于其可变性（风险）的大小）来评估北美西海岸的奇努克和红鲑鱼投资组合的表现。我们从每个投资组合中鲑鱼收益的方差和协方差评估了对投资组合绩效的影响，以及投资组合绩效与分水岭属性之间的关联。我们发现，奇努克和红鲑鱼投资组合的风险调整后表现呈积极的纬度趋势，这也与人为对流域的影响（例如水坝和土地利用变化）呈负相关。高纬度奇努克鲑鱼组合平均可靠2·5倍，他们的投资组合风险主要是由于单项资产的低方差。在高纬度地区，马哈鱼的投资组合也更可靠，但在表现最好的投资组合中，风险来源各不相同。合成与应用。投资组合理论为描述鲑鱼生态系统及其服务的恢复力提供了一种简单的方法。未开发流域之间投资组合绩效的自然变化为恢复工作提供了基准。在当地和地区，评估投资组合风险的来源可以指导行动，以保持现有的弹性（保护栖息地和干扰制度，保持响应多样性；采用对不同投资组合成分敏感的收获策略）或改善恢复活动。提高我们对投资组合可靠性的理解可能允许对自然资源进行管理，以适应持续的环境变化。投资组合理论为描述鲑鱼生态系统及其服务的恢复力提供了一种简单的方法。未开发流域之间投资组合绩效的自然变化为恢复工作提供了基准。在当地和地区，评估投资组合风险的来源可以指导行动，以保持现有的弹性（保护栖息地和干扰制度，保持响应多样性；采用对不同投资组合成分敏感的收获策略）或改善恢复活动。提高我们对投资组合可靠性的理解可能允许对自然资源进行管理，以适应持续的环境变化。
