Faculty of Environmental Sciences, Community Ecology & Conservation, Czech University of Life Sciences Prague, Prague 6, Czech Republic.
Institute of Biological Sciences, University of Zielona Góra, Zielona Góra, Poland.
J Anim Ecol. 2021 Aug;90(8):1844-1853. doi: 10.1111/1365-2656.13498. Epub 2021 May 25.
The main objective of this long-term study (1978-2016) was to find the underlying factors behind the declining trends of eider Somateria mollissima in the Baltic/Wadden Sea. Specifically, we aimed at quantifying the bottom-up effect of nutrients, through mussel stocks, on reproduction and abundance of eider, and the top-down effects caused by white-tailed eagle Haliaeetus albicilla predation. Bottom-up effects increase marine primary productivity with subsequent effects on food availability for a major mussel predator. Top-down effects may also regulate eider populations because during incubation female eiders are vulnerable to predation by eagles. Our structural equation modelling explained a large percentage of the variance in eider abundance. We conclude that the Baltic/Wadden Sea eider population was regulated directly by white-tailed sea eagle predation on incubating females and indirectly by the amount of nutrients in seawater affecting both mussel stocks and the breeding success of eiders, reflecting density dependence. These findings may explain the decreasing trend in the Baltic/Wadden Sea eider population during the last decades as an additive effect of top-down and bottom-up factors, and likely as an interaction between them.
本长期研究（1978-2016 年）的主要目的是找出波罗的海/瓦登海（Baltic/Wadden Sea）的绒鸭 Somateria mollissima 数量下降的潜在因素。具体而言，我们旨在量化通过贻贝存量产生的营养物质的下行效应，对绒鸭繁殖和丰度的影响，以及白尾海雕（Haliaeetus albicilla）捕食造成的上行效应。下行效应增加了海洋初级生产力，继而对主要贻贝捕食者的食物供应产生影响。上行效应也可能对绒鸭种群进行调节，因为在孵化期间，雌性绒鸭易受到鹰类的捕食。我们的结构方程模型解释了绒鸭丰度变化的很大一部分。我们的结论是，波罗的海/瓦登海的绒鸭种群直接受到白尾海雕对正在孵蛋的雌鸟的捕食，以及通过海水养分含量的间接影响，这些养分含量影响贻贝存量和绒鸭的繁殖成功率，反映了密度依赖性。这些发现可能解释了过去几十年里波罗的海/瓦登海绒鸭数量下降的趋势，这是由于上行和下行因素的附加效应，可能是它们之间的相互作用。
