Urbanization results in major changes in stream morphology, hydrology, and water quality; the consequences on fish assemblage of Neotropical urban streams remain poorly understood. Due to the importance of better understanding fish assemblage responses towards urbanization in biodiversity hotspots, we evaluated the factors structuring the fish assemblages in a Neotropical medium-sized city. Additionally, we evaluated possible differences in fish diversity and biotic homogenization between the urban and control streams. To do so, fish were sampled along with physical habitat and water quality parameters in 16 urban streams in southern Brazil. Multiple regression and distance-based linear models (DistLM) were used to assess the importance of predictor variables in determining species richness and fish assemblage composition, respectively. The fish abundance rank curves were plotted to evaluate graphic differences in fish diversity between urban and control streams, while the relationship between distance and similarity (Bray-Curtis index) was used to evaluate biotic homogenization. The results revealed the importance of variables linking habitat diversity and basin connectivity to fish assemblage richness and structure. In addition, riparian vegetation was the main driver of fish assemblages, explaining 78% of abundance variation. We identified lower diversity and higher biotic homogenization in urban streams, with higher dominance of the non-native species Poecilia reticulata. Our results highlight the importance of evaluating the physical and biotic variables of streams outside of water pollution levels alone. Finally, it is necessary to support urban planning practices that recover riparian vegetation, avoid canalization, and promote connectivity along stream networks as well as the removal of artificial structures in urban basins.

中文翻译：

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新热带城市流域鱼群结构的驱动因素

城市化导致河流形态，水文和水质发生重大变化。人们对新热带城市溪流对鱼类聚集的影响知之甚少。由于必须更好地了解生物多样性热点地区鱼群对城市化的响应，我们评估了构成新热带中型城市鱼群的因素。此外，我们评估了城市和控制流之间鱼类多样性和生物均质化的可能差异。为此，在巴西南部的16条城市溪流中对鱼类以及物理栖息地和水质参数进行了采样。多元回归和基于距离的线性模型（DistLM）分别用于评估预测变量在确定物种丰富度和鱼类种群组成中的重要性。绘制鱼类丰度等级曲线以评估城市和控制流之间鱼类多样性的图形差异，而距离和相似性之间的关系（Bray-Curtis指数）用于评估生物均质性。结果表明，将生境多样性和流域连通性与鱼类种群的丰富度和结构联系起来的变量的重要性。此外，河岸植被是鱼类聚集的主要驱动力，解释了78％的丰度变化。我们确定了城市溪流中较低的多样性和较高的生物同质化水平，其中非本地物种的优势较高 而距离和相似度之间的关系（Bray-Curtis指数）用于评估生物同质化。结果表明，将生境多样性和流域连通性与鱼类种群的丰富度和结构联系起来的变量的重要性。此外，河岸植被是鱼类聚集的主要驱动力，解释了78％的丰度变化。我们确定了城市溪流中较低的多样性和较高的生物同质化水平，其中非本地物种的优势较高 而距离和相似度之间的关系（Bray-Curtis指数）用于评估生物同质化。结果表明，将生境多样性和流域连通性与鱼类种群的丰富度和结构联系起来的变量的重要性。此外，河岸植被是鱼类聚集的主要驱动力，解释了78％的丰度变化。我们确定了城市溪流中较低的多样性和较高的生物同质化水平，其中非本地物种的优势较高网状的Poecilia。我们的结果强调了仅评估水污染水平以外的溪流的物理和生物变量的重要性。最后，有必要支持城市规划实践，以恢复河岸植被，避免渠化，促进沿河网的连通性以及拆除城市盆地中的人工结构。