Depending on the life cycles of trophic biota, cascades of biological transition are established between top-down and bottom-up relationship. In South Korea, flows of the large rivers have been regulated with large weirs and estuary barrages construction. The Eurasian otter Lutra lutra is a semi-aquatic carnivore and top predator in freshwater systems. In order to understand the aquatic community variability under the impact of river modifications, we assessed the strengths of otter populations in relation to limnological data monitored between 2014 and 2016 at 250 sites of the Nakdong River, 92 sites of the Yeongsan River and 81 sites of the Seumjin River. The habitat preference and resource use of otter populations have been measured for each of the 423 river sites by the number of spraint (= otters' feces) per 600 m. The limnological data included water quality parameters, abundances of Mollusca, Anthropoda, Annelida, Nematomorpha, and Platyhelminthes as well as abundances of benthivore, herbivore, planktivore and piscivore fish. The hybrid evolutionary algorithm HEA has been applied to model relationships of otter with water quality, the benthic invertebrates and fish to determine habitat and food preferences of otter across the three rivers.

Despite the stochastic noise of the data, the modelling results addressed well relationships between spraint densities and densities of fish and macroinvertebrate communities. Threshold conditions of the IF-THEN-ELSE-models discovered by HEA revealed otter responses to changing habitats and aquatic communities across the river sites but also between the three rivers. In addition, sensitivity analysis suggested possible relationships between the otter and aquatic communities. According to the results of sensitivity analysis, otter populations seemed not to control the piscivorous fish densities by showing a negative relationship, but preyed preferably on benthivorous and planktivorous fishes. Water quality parameters and benthic macro-invertebrates correlated well with otter populations suggesting favorable habitat and food-web structures. There is evidence that river flow regulation measures have a negative impact on otter populations, and that growing otter populations will alter future food web structures of the three rivers.

根据营养生物群的生命周期，在自上而下和自下而上的关系之间建立了生物过渡级联。在韩国，大型河流的水流已通过大型堰和河口拦河坝的建设进行了调节。欧亚水獭Lutra lutra是淡水系统中的半水生食肉动物和顶级捕食者。为了了解河道改造的影响下水生群落的多样性，我们评估了在2014年至2016年之间的那东河250个站点，龙山河92个站点和永隆河81个站点所监测的水獭数据的强度。胜金河 根据每600 m的扭伤数（=水獭的粪便），对423个河流站点中的每一个进行了水獭种群栖息地偏好和资源利用的测量。湖泊学数据包括水质参数，软体动物，拟人脚纲，猫科动物，线虫和侧柏的丰富度，以及底栖动物，草食动物，浮游动物和食肉动物的丰富度。

尽管数据是随机的，但是建模结果很好地解决了扭伤密度与鱼类和大型无脊椎动物群落密度之间的关系。HEA发现的IF-THEN-ELSE模型的阈值条件揭示了水獭对跨河站点以及三河之间不断变化的栖息地和水生群落的反应。此外，敏感性分析表明水獭与水生群落之间可能存在联系。根据敏感性分析的结果，水獭种群似乎并没有通过显示负相关关系来控制食肉鱼类的密度，而是以弯食性和浮游性鱼类为食。水质参数和底栖大型无脊椎动物与水獭种群相关性很好，表明其有利的栖息地和食物网结构。