Water flow velocity is a strong environmental filter structuring benthic communities in lotic ecosystems. While many studies have determined its effect on the distribution and diversity patterns of insects, the role of water flow velocity on other groups of aquatic invertebrates (i.e., Oligochaeta) has remained unexplored. We sampled five lotic ecosystems to investigate the influence of water flow velocity on the species composition of Oligochaeta assemblages in a Neotropical floodplain. Our first hypothesis was that higher water flow velocity decreases Oligochaeta assemblages variability. Consequently, we expected a lower beta diversity among the mid-channels of the ecosystems (i.e., sites with higher water velocity) relative to channel margins (i.e., sites with lower water velocity). Our second hypothesis was that water flow velocity determines species composition of Oligochaeta. Consequently, we expected a different species composition between the mid-channel and the channel margins of lotic ecosystems. We found 19 Oligochaeta species across the five lotic ecosystems. We corroborated both hypotheses because we found lower Oligochaeta beta diversity among the mid-channels of the lotic ecosystems as well as a different species composition. Haplotaxis aedeochaeta and Narapa bonettoi were the taxa strongly associated with the mid-channel, because they are adapted to live among the sand grains in the bottom of the rivers with high depth and water velocity. Overall, water flow velocity should be considered as a strong driver of Oligochaeta species composition.

中文翻译：

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高水流速降低了β多样性，并导致了新热带抽水生态系统中Oligochaeta的独特组成

水流速度是在抽水生态系统中构造底栖生物群落的强大环境过滤器。尽管许多研究已经确定了其对昆虫分布和多样性格局的影响，但水流速度对其他种类的水生无脊椎动物（即Oligochaeta）的作用尚待探索。我们采样了五个抽水生态系统，以研究水流速对新热带洪泛区中Oligochaeta组合物种组成的影响。我们的第一个假设是较高的水流速会降低Oligochaeta组合的可变性。因此，我们预计，相对于河道边缘（即水速较低的地点），生态系统中部通道（即水速较高的地点）的β多样性较低。我们的第二个假设是水流速决定了Oligochaeta的物种组成。因此，我们期望在Lotic生态系统的中通道和通道边缘之间存在不同的物种组成。我们在五个水生态系统中发现了19种Oligochaeta物种。我们证实了这两个假设，因为我们发现在抽水生态系统的中间渠道之间存在较低的Oligochaetaβ多样性，并且物种组成不同。Haplotaxis aedeochaeta和Narapa bonettoi是与中游河道密切相关的分类单元，因为它们适合生活在河床深处且水流速度较高的沙粒中。总体而言，应将水流速度视为Oligochaeta物种组成的重要驱动因素。