The distribution area of a species is determined by a combination of factors and since each species of aquatic insect has adapted to drastically changing environments along river channels, they are excellent targets for study. Considering these factors, we focused on three Ephemera mayflies inhabiting the Japanese Archipelago and investigate their niche differentiation patterns. A total of 29 study sites were established within the Asahi-gawa River System to study the relationship between various environmental factors and these mayflies' population structures. From the results of RDA and/or GLMMs, Ephemera japonica tended to distribute in locations with a small degree of canopy openness and a lot of cobbles and boulders. In contrast, Ephemera orientalis tended to distribute in locations with small riverbed slope degree, and small grain size. The distribution area of Ephemera strigata was intermediate between that of E. japonica and E. orientalis. At several study sites, although the distribution patterns appeared irregular due to surrounding environments affected by artificial structures, these patterns can be explained by examining the environmental factors around dams. These results on geographical fine-scaled niche differentiation within a closely related species provide significance knowledge to support understanding of the mechanisms of species coexistence and biodiversity creation.

一个物种的分布区域是由多种因素决定的，由于每种水生昆虫都适应了河道沿线急剧变化的环境，因此它们是极好的研究目标。考虑到这些因素，我们重点研究了居住在日本群岛的三种蜉蝣蜉蝣，并研究了它们的生态位分化模式。在旭川系统内共设立了 29 个研究地点，以研究各种环境因素与这些蜉蝣种群结构之间的关系。从 RDA 和/或 GLMMs 的结果来看，蜉蝣倾向于分布在冠层开放度较小和大量鹅卵石和巨石的位置。相比之下，蜉蝣多分布于河床坡度较小、粒度较小的地区。蜉蝣分布区介于粳稻和东方蜉蝣之间。在几个研究地点，虽然由于周围环境受人工结构影响，分布模式显得不规则，但这些模式可以通过检查大坝周围的环境因素来解释。这些关于密切相关物种内地理细尺度生态位分化的结果为支持理解物种共存和生物多样性创造的机制提供了重要知识。