Effect of land-use types on the ecomorphological structure of fish assemblage in distinct mesohabitats of neotropical streams

Abstract The use and occupation of land by human population substantially influence environmental variables and fish assemblage in streams. However, there is little knowledge on how these changes affect the ecomorphological structure of fish assemblage in mesohabitats. Therefore, we aim to assess whether the land-use types affect the ecomorphological structure of fish assemblage in distinct mesohabitats. Environmental and ichthyofaunistic data were collected in three mesohabitats (rifles, runs, and pools) of five rural and five urban streams. Twenty-one ecomorphological indices were obtained from the mean of linear morphological measurements and areas of the fishes. Subsequently, the Euclidean distance was calculated, based on the ecomorphological indices, between each pair of species, to measure the ecomorphological distances for the mesohabitats of the rural and urban streams. The results show that the urban environment is more harmful to streams than the rural one, due to changes in the environmental variables and decrease in species richness. The main environmental changes found in urban streams were the decrease in canopy cover by riparian vegetation and dissolved oxygen, and the increase in electrical conductivity and bed silting. Also, there was a significant decrease in the morphological similarity between fish species in the mesohabitats of urban streams compared to rural ones. Therefore, we can conclude that the urban environment leads to the loss of morphologically similar fish species in the mesohabitats, with only a few functionally distinct species remaining.

摘要 人类对土地的利用与占用，会显著影响溪流的环境变量与鱼类群落组成。然而目前学界对这类变化如何作用于中型生境（mesohabitat）中鱼类群落的生态形态结构仍知之甚少。因此本研究旨在探究土地利用类型是否会对不同中型生境下的鱼类群落生态形态结构产生影响。研究于5条乡村溪流与5条城市溪流的3类中型生境（急滩、缓流区与深潭）中采集了环境数据与鱼类区系资料。研究人员基于鱼类的线性形态测量值与体表面积，计算得到21项生态形态学指标。随后基于各物种间的生态形态学指标，计算欧氏距离（Euclidean distance），以此衡量乡村与城市溪流各中型生境的生态形态差异。研究结果显示，相较于乡村溪流，城市环境对溪流的负面影响更为显著，具体体现为环境变量发生改变以及物种丰富度（species richness）下降。城市溪流中观测到的主要环境变化包括：河岸植被（riparian vegetation）冠层覆盖率降低、溶解氧（dissolved oxygen）浓度下降，同时电导率（electrical conductivity）与河床淤积（bed silting）程度升高。此外，相较于乡村溪流的中型生境，城市溪流中型生境中鱼类物种间的形态相似性出现了显著下降。综上，本研究认为城市环境会导致中型生境中形态相似的鱼类物种流失，仅存少数功能特征迥异的物种。