Abstract Dams change the hydrological dynamics, patterns of biological production and distribution of organisms in space and time. In contrast, tributary rivers can function as source areas in reservoirs, since they harbor spawning and early development grounds for native fish species. Here, we analyze a time series of the first 14 years after the impoundment of the Porto Primavera Reservoir, a large reservoir with free tributaries in southeastern Brazil. To evaluate the impact of damming on the fish assemblage, we evaluated the abundance (catch per unit effort, CPUE) and α (species richness and Shannon-Wiener index) and β (Sorensen dissimilarity and turnover) diversity of four sites distributed along the reservoir. Overall, there was no decreasing trend in the α diversity and no increasing trend in the β diversity relative to the initial year or among the sites over time. Despite the expected disturbance in the fish assemblage at the lacustrine site, the sites located near the tributary mouths presented resistant fish assemblages, compensating the results of the overall assessment. We attribute this unusual variation in the ecological attributes to source-sink demographic dynamics, with the undammed tributaries as the source and the reservoir as the sink for native species. We highlight that the presence of these rivers minimized the expected trend towards biotic homogenization, and the preservation of the tributaries is imperative since they contribute to diversity maintenance in areas that are already impacted by damming. The inclusion of this agenda in environmental management programs and new impoundment plans will allow a balance between the demand for electricity production and the conservation of fish diversity.

中文翻译：

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无坝支流对保护新热带水库鱼类生物多样性的重要性

摘要 大坝改变了水文动力学、生物生产模式以及生物在空间和时间上的分布。相比之下，支流河流可以作为水库的源区，因为它们为本地鱼类提供产卵和早期发育场所。在这里，我们分析了 Porto Primavera 水库蓄水后前 14 年的时间序列，该水库是巴西东南部具有自由支流的大型水库。为了评估筑坝对鱼类群落的影响，我们评估了沿水库分布的四个地点的丰度（每单位努力的渔获量，CPUE）和 α（物种丰富度和香农-维纳指数）和 β（索伦森差异和周转）多样性. 全面的，α多样性没有下降趋势，β多样性相对于初始年份或随着时间的推移没有增加趋势。尽管湖区鱼类群落预计会受到干扰，但位于支流口附近的地点出现了抗性鱼类群落，弥补了总体评估的结果。我们将生态属性的这种不寻常变化归因于源汇人口动态，以未建坝的支流为源，水库为本地物种的汇。我们强调，这些河流的存在最大限度地减少了生物同质化的预期趋势，并且支流的保护势在必行，因为它们有助于已经受到大坝影响的地区的多样性维护。