Department of Arctic Ecology, Norwegian Institute for Nature Research (NINA), Fram Centre, Tromsø, Norway.
PLoS One. 2011;6(7):e22729. doi: 10.1371/journal.pone.0022729. Epub 2011 Jul 28.
In a "wasp-waist" ecosystem, an intermediate trophic level is expected to control the abundance of predators through a bottom-up interaction and the abundance of prey through a top-down interaction. Previous studies suggest that the North Sea is mainly governed by bottom-up interactions driven by climate perturbations. However, few studies have investigated the importance of the intermediate trophic level occupied by small pelagic fishes.
METHODOLOGY/PRINCIPAL FINDINGS: We investigated the numeric interactions among 10 species of seabirds, two species of pelagic fish and four groups of zooplankton in the North Sea using decadal-scale databases. Linear models were used to relate the time series of zooplankton and seabirds to the time series of pelagic fish. Seabirds were positively related to herring (Clupea harengus), suggesting a bottom-up interaction. Two groups of zooplankton; Calanus helgolandicus and krill were negatively related to sprat (Sprattus sprattus) and herring respectively, suggesting top-down interactions. In addition, we found positive relationships among the zooplankton groups. Para/pseudocalanus was positively related to C. helgolandicus and C. finmarchicus was positively related to krill.
CONCLUSION/SIGNIFICANCE: Our results indicate that herring was important in regulating the abundance of seabirds through a bottom-up interaction and that herring and sprat were important in regulating zooplankton through top-down interactions. We suggest that the positive relationships among zooplankton groups were due to selective foraging and switching in the two clupeid fishes. Our results suggest that "wasp-waist" interactions might be more important in the North Sea than previously anticipated. Fluctuations in the populations of pelagic fish due to harvesting and depletion of their predators might accordingly have profound consequences for ecosystem dynamics through trophic cascades.
在“蜂腰”生态系统中，中间营养级预计将通过自上而下的相互作用控制捕食者的丰度，通过自下而上的相互作用控制猎物的丰度。先前的研究表明，北海主要受气候波动驱动的底层相互作用控制。然而，很少有研究调查小型洄游鱼类占据的中间营养级的重要性。
方法/主要发现：我们利用数十年的数据库，调查了北海 10 种海鸟、两种洄游鱼类和 4 组浮游动物之间的数值相互作用。线性模型用于将浮游动物和海鸟的时间序列与洄游鱼类的时间序列相关联。海鸟与鲱鱼（Clupea harengus）呈正相关，表明存在自下而上的相互作用。两组浮游动物；拟哲水蚤和磷虾分别与鲱鱼和鲱鱼呈负相关，表明存在自上而下的相互作用。此外，我们还发现浮游动物组之间存在正相关关系。假磷虾与拟哲水蚤呈正相关，长额拟磷虾与磷虾呈正相关。
结论/意义：我们的结果表明，鲱鱼通过自下而上的相互作用对海鸟的丰度具有重要的调节作用，而鲱鱼和鲱鱼通过自上而下的相互作用对浮游动物具有重要的调节作用。我们认为，两组浮游动物之间的正相关关系是由于两种鲱鱼的选择性觅食和转换。我们的研究结果表明，“蜂腰”相互作用在北海可能比以前预期的更为重要。由于捕捞和捕食者的枯竭而导致的洄游鱼类种群的波动，可能会通过营养级联对生态系统动态产生深远的影响。
