College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, 17101 Point Lena Loop Road, Juneau, Alaska, 99801, USA.
Status of Stocks and Multispecies Assessment Program, Alaska Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Bldg 4, Seattle, Washington, 98115, USA.
Ecol Appl. 2020 Oct;30(7):e02141. doi: 10.1002/eap.2141. Epub 2020 Jul 31.
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.
捕食对生态重要的猎物的种群动态可能产生重大且长期的影响。然而，当捕食者的消耗不同步时，多样化的捕食者组合可能会对猎物的死亡率产生稳定（即组合）效应。我们计算了主要饲料物种捕食的时空变化，以量化食物网背景下的同步性和组合效应，并更好地理解经历群落组成重大变化的大型海洋生态系统中的多样性-稳定性关系。我们选择大眼狮鲈（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，并作为一系列经济和文化上重要物种的重要猎物。因此，有足够的数据可以用来在实证环境中测试大眼狮鲈的生态理论。空间明确的捕食指数考虑了阿拉斯加湾（1990-2015 年）中捕食者生物量、基于生物能量的定量供应以及一系列底栖鱼类消耗的特定年龄组大眼狮鲈的年度变化。我们发现，箭齿鲽（Atheresthes stomias）是迄今为止最主要的大眼狮鲈捕食者（比例消耗：0.74±0.14）。我们还发现捕食者物种之间存在同步趋势，表明在流域尺度上缺乏组合效应。这种单一优势捕食者和同步消耗动态的组合表明，在阿拉斯加湾对大眼狮鲈的控制非常强烈，尽管在所有空间尺度上的同步性变化很大。虽然同步性通常在西部子区域增加，但随着时间的推移，在阿拉斯加湾中部的消费变得不那么同步。这表明一个地区的营养稳定性降低，另一个地区的稳定性增加，从而强调了保持食物网结构和功能的时空异质性的重要性。最后，大眼狮鲈的总消耗量变化很大（范围从 1.87 到 7.63 太吨），并且经常超过基于评估的生产力估计值。我们断言，将我们整体的、经验得出的捕食指数作为假设的自然死亡率常数的修正因子，将为将生态信息纳入单一物种种群评估提供一种实用方法。
