Predation can have substantial and long‐term effects on the population dynamics of ecologically important prey. Diverse predator assemblages, however, may produce stabilizing (i.e., portfolio) effects on prey mortality when consumption varies asynchronously among predators. We calculated spatiotemporal variation in predation on a dominant forage species to quantify synchrony and portfolio effects in a food web context and better understand diversity–stability relationships in a large marine ecosystem that has undergone considerable changes in community composition. We selected Walleye Pollock (Gadus chalcogrammus) as our case study because they support some of the largest, most valuable commercial fisheries in the world and serve as essential prey for an array of economically and culturally important species. Thus, there are sufficient data for Pollock with which to test ecological theories in an empirical setting. Spatially explicit predation indices accounted for annual variation in predator biomass, bioenergetics‐based rations, and age‐specific proportions of Pollock consumed by a suite of groundfishes in the Gulf of Alaska (1990–2015). We found that Arrowtooth Flounder (Atheresthes stomias) was, by far, the dominant Pollock predator (proportional consumption: 0.74 ± 0.14). We also found synchronous trends in consumption among predator species, indicating a lack of portfolio effects at the basin scale. This combination of a single dominant predator and synchronous consumption dynamics suggests strong top‐down control over Pollock in the Gulf of Alaska, though the degree of synchrony was highly variable at all spatial scales. Whereas synchrony generally increased in the western subregion, consumption in the central Gulf of Alaska became less synchronous through time. This suggests diminished trophic stability in one area and increased stability in another, thereby emphasizing the importance of spatiotemporal heterogeneity in maintaining food web structure and function. Finally, total Pollock consumption was highly variable (ranging from 1.87 to 7.63 Tg) and often exceeded assessment‐based estimates of productivity. We assert that using our holistic and empirically derived predation index as a modifier of assumed constant natural mortality would provide a practical method for incorporating ecological information into single‐species stock assessments.

中文翻译：

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开发捕食指数以评估阿拉斯加湾的营养稳定性。

捕食会对具有生态重要性的猎物的种群动态产生重大而长期的影响。但是，当捕食者之间的消费量异步变化时，多样化的捕食者组合可能会对猎物死亡率产生稳定的影响（即投资组合）。我们计算了主要牧草物种在捕食中的时空变化，以量化食物网背景下的同步性和投资组合效应，并更好地了解在群落组成发生了巨大变化的大型海洋生态系统中，多样性与稳定性之间的关系。我们选择了Walleye Pollock（Gadus chalcogrammus）作为我们的案例研究，因为它们支持世界上一些最大，最有价值的商业渔业，并且是一系列具有重要经济和文化意义的物种的重要猎物。因此，有足够的数据可用于Pollock在经验背景下检验生态学理论。空间明确的捕食指数说明了阿拉斯加湾（1990-2015年）一组底层鱼类所消耗的捕食者生物量，基于生物能学的定量以及特定年龄比例的波洛克的年度变化。我们发现箭牙比目鱼（Atheresthes stomias）到目前为止是主要的波洛克捕食者（比例消耗：0.74±0.14）。我们还发现了捕食物种之间的消费同步趋势，表明在流域规模上缺乏投资组合效应。单一优势捕食者和同步消费动态的结合表明，对阿拉斯加湾的波洛克进行了强有力的自上而下的控制，尽管同步程度在所有空间尺度上都是高度可变的。西部次区域的同步性总体上有所提高，而阿拉斯加中部海湾的消费随着时间的推移变得不那么同步。这表明一个区域的营养稳定性下降，而另一区域的营养稳定性增加，从而强调时空异质性在维持食物网结构和功能方面的重要性。最后，Pollock的总消费量变化很大（范围从1.87 Tg到7.63 Tg），经常超过基于评估的生产率估计值。我们断言，将我们的整体和经验得出的捕食指数用作假定的恒定自然死亡率的修正数，将为将生态信息纳入单物种种群评估提供一种实用的方法。