Fish community structure and nested distribution pattern of the three tributaries at the head of the Three Gorges Reservoir

群落结构和分布格局是群落生态学研究的核心问题之一。为了解三峡库区支流鱼类群落现状和分布格局，2020—2021年对三峡库首的香溪河、袁水河和青干河3条支流的鱼类群落进行调查，运用嵌套模型探讨了鱼类群落的分布格局。在三峡库首3条支流共采集到鱼类60种，隶属于7目13科44属，均以短颌鲚（Coilia brachygnathus）、似鳊（Pseudobrama simoni）和贝氏䱗（Hemiculter bleekeri）等为优势种。季节上，3条支流短颌鲚、似鳊和贝氏䱗等优势种的相对丰度在夏季高于秋季（袁水河似鳊除外）。空间上，支流河口江段短颌鲚、似鳊和飘鱼（Pseudolaubuca sinensis）等相对丰度较高，而下游江段短颌鲚、贝氏䱗和达氏鮊（Culter dabryi）等相对丰度较高。Cluster分析和NMDS分析表明，三峡库首3条支流鱼类群落的季节变化大于空间变化。SIMPER分析显示，鱼类群落结构不同季节组间相异性为49.7%，主要贡献种为短颌鲚和似鳊，贡献率分别为17.5%和15.8%。嵌套模型分析显示，三峡库首香溪河、袁水河和青干河3条支流鱼类群落呈现显著的季节嵌套性分布格局，秋季鱼类群落是夏季鱼类群落的子集；空间上，夏季鱼类群落嵌套性分布显著，秋季不显著。;Community structure and distribution patterns are among the core issues in community ecology research. To understand the current status and distribution patterns of fish communities in the tributaries of the Three Gorges Reservoir, a survey of fish communities in the Xiangxi River, Yuanshui River, and Qinggan River, the three tributaries at the head of the Three Gorges Reservoir, was conducted from 2020 to 2021. A nested model was applied to explore the distribution patterns of the fish communities. A total of 60 fish species belonging to 7 orders, 13 families, and 44 genera were collected in the three tributaries at the head of the Three Gorges Reservoir. The dominant species in the three tributaries were Coilia brachygnathus, Pseudobrama simoni, and Hemiculter bleekeri. Seasonally, the relative abundance of dominant species such as Coilia brachygnathus, Pseudobrama simoni, and Hemiculter bleekeri was higher in summer than in autumn (except for Pseudobrama simoni in the Yuanshui River). Spatially, the relative abundance of species such as Coilia brachygnathus, Pseudobrama simoni, and Pseudolaubuca sinensis was higher in the estuary sections. In comparison, the relative abundance of Coilia brachygnathus, Hemiculter bleekeri, and Culter dabryi was higher in the downstream sections. Cluster and NMDS analysis indicated that the seasonal changes in fish communities in the three tributaries at the head of the Three Gorges Reservoir were greater than spatial changes. The SIMPER analysis showed that the dissimilarity between different seasonal groups of fish community structure was 49.7%, with the main contributing species being Coilia brachygnathus and Pseudobrama simoni, contributing 17.5% and 15.8%, respectively. Nested model analysis revealed a significant seasonal nested distribution pattern in the fish communities of the Xiangxi River, Yuanshui River, and Qinggan River at the head of the Three Gorges Reservoir, with the fish community in autumn being a subset of that in summer; spatially, the nested distribution of fish communities was significant in summer but not in autumn.