Long-term effects of a rural landscape on the structure and trophic organization of a fish assemblage

Abstract Aim We investigated the long-term effects of a rural landscape on the structure and trophic organization of a fish assemblage. Methods We compared environmental data and data from fish assemblage structure and trophic organization sampled in a stream located in a rural area, within a time gap of 20 years. Results We observed only punctual changes in the environmental variables and fish structure, which may not be related to the rural landscape. In fish diet, insectivory remained predominant in all sample periods. However, when we analyzed the groups of hexapods consumed by the fish species, we found a substitution of Ephemeroptera and Trichoptera by Diptera over time. Conclusions Although the fish assemblage structure was not affected, the insectivore diet analysis showed that the stream stretch could be in an ongoing process of environmental quality loss, once the simplification in the macroinvertebrates assemblage structure over time is indicative of environmental degradation.

### 摘要
#### 研究目的
本研究旨在探究农村景观对鱼类群落（fish assemblage）结构与营养组织的长期影响。
#### 研究方法
我们以20年为时间间隔，对一处位于农村区域的溪流开展了两次采样，采集了环境数据以及鱼类群落结构与营养组织的相关数据，并对其进行了对比。
#### 研究结果
我们仅观察到环境变量与鱼类群落结构存在零星变化，且此类变化可能与农村景观无关。在鱼类食性方面，所有采样时期均以食虫性为主要摄食类型。然而，当分析鱼类所摄食的六足类类群时，我们发现随着时间推移，蜉蝣目（Ephemeroptera）与毛翅目（Trichoptera）类群被双翅目（Diptera）所替代。
#### 研究结论
尽管鱼类群落结构未受显著影响，但食性分析结果表明，该溪流段可能正处于环境质量持续退化的进程中：大型无脊椎动物（macroinvertebrates）群落结构随时间发生简化，这一现象是环境退化的典型指示标志。