Fish assemblage composition of the four basins of Wannan Mountains, China

Extensive distribution of widespread species and the loss of native species driven by anthropogenic disturbances modify community similarity, resulting in a decrease or increase in community distinctiveness. Data from four basins in the Wannan Mountains, China, were used to evaluate the effects of low-head dams on patterns of fish faunal homogenization and differentiation based on abundance data. We aimed to examine the spatial changes in taxonomic and functional similarities of fish assemblages driven by low-head dams and whether the changes in the similarity of fish assemblages differed between taxonomic and functional components. We found that low-head dams significantly decreased the mean taxonomic similarity but increased the mean functional similarity of fish assemblages in impoundments using abundance-based approaches, suggesting that taxonomic differentiation accompanied functional homogenization in stream fish assemblages. These results show the importance of population abundance in structuring fish faunal homogenization and differentiation at small scales, especially when the major differences among assemblages are in species abundance ranks rather than species identities. Additionally, we also found only a weak positive correlation between changes in mean taxonomic and functional similarities, and partial pairs exhibited considerable variation in patterns of fish faunal homogenization and differentiation for taxonomic and functional components. In conclusion, this study highlighted that the observed taxonomic differentiation of current fish assemblages (short-term phenomenon) is probably an early warning sign of further homogenization in regions where native species are completely predominated, and that changes in taxonomic similarity cannot be used to predict changes in functional similarity. Keywords: Low-head dam, Stream fish, Biotic homogenization and differentiation, Taxonomic and functional diversities

广布种的广泛扩散与人为干扰介导的本土物种丧失，会改变群落相似性，进而导致群落独特性出现升降变化。本研究以中国皖南山区四个流域的物种丰度数据为基础，评估低水头坝（Low-head dam）对鱼类区系同质化与分化（fish faunal homogenization and differentiation）格局的影响。本研究旨在探究低水头坝驱动下鱼类集合群（fish assemblages）的分类学相似性与功能相似性的空间变化特征，同时验证鱼类集合群的相似性变化在分类学与功能维度间是否存在显著差异。基于丰度分析方法，本研究发现低水头坝会显著降低拦蓄库区鱼类集合群的平均分类学相似性，却提升其平均功能相似性，这表明溪流鱼类集合群中分类学分化与功能同质化相伴发生。上述结果揭示了种群丰度在小尺度下塑造鱼类区系同质化与分化格局的重要性，尤其当集合群间的核心差异体现为物种丰度排序而非物种组成本身时。此外，本研究还发现，鱼类集合群的平均分类学相似性变化与功能相似性变化之间仅存在微弱的正相关，且部分配对样本的鱼类区系在分类学与功能维度上的同质化与分化格局存在显著异质性。综上，本研究表明：当前观测到的鱼类集合群分类学分化（短期现象），在本土物种占据绝对优势的区域，可能是未来进一步发生区系同质化的早期预警信号；同时，分类学相似性的变化无法用于预测功能相似性的变化。关键词：低水头坝（Low-head dam）、溪流鱼类、生物区系同质化与分化（biotic homogenization and differentiation）、分类学与功能多样性（taxonomic and functional diversities）