The impacts of water level fluctuations between wet and dry seasons on taxonomic and functional diversity of fish communities in the ecotone floodplain of Lake Caizi

Abstract

水位的洪枯变化通过江湖连通影响泛滥平原湖泊鱼类的组成和分布，因而江湖过渡带是反映泛滥平原生态系统鱼类交流和多样性变动的关键区域.尽管如此，针对江湖过渡带鱼类群落随水位洪枯变化的研究十分匮乏.本研究以菜子湖江湖过渡带为例，分别在洪水和枯水期选取包括静水和流水生境的样点对鱼类群落进行系统的调查采样，探讨水位洪枯变化对菜子湖江湖过渡带鱼类物种和功能多样性的影响.共采集到鱼类6目12科37属52种，其中，洪水期和枯水期物种数差异显著，分别采集到鱼类50和42种，而静水生境和流水生境物种数差异不明显，分别采集到鱼类47和48种.与洪水期相比，枯水期山溪河流性鱼类的物种数、重量、尾数和优势度百分比分别减少了7.3%、6.3%、14.4%和12.0%；与静水生境相比，流水生境山溪河流性鱼类的物种数、重量、尾数和优势度百分比分别增加了5.3%、14.6%、18.0%和22.3%.SIMPER分析结果显示，麦穗鱼（Pseudorasbora parva）、蛇鮈（Saurogobio dabryi）、（Hemiculter leucisculus）、鲤（Cyprinus carpio）、鲫（Carassius auratus）、短颌鲚（Coilia brachygnathus）、似鳊（Pseudobrama simoni）、翘嘴鲌（Culter ilishaeformis）、达氏鲌（Culter dabryi）、光唇蛇鮈（Saurogobio gymnocheilus）和无须鱊（Acheilognathus gracilis）是引起水位洪枯变化以及不同生境类型鱼类群落结构差异的主要物种.优势度分析结果表明枯水期和静水生境的优势种鱼类相似，重要值较高的优势种鱼类为鲤、鲫、和似鳊；而洪水期和流水生境的优势种鱼类同样相似，重要值较高的优势种鱼类为麦穗鱼、蛇鮈、光唇蛇鮈和短颌鲚.通过双因素方差分析解析了水位洪枯变化和不同生境类型对鱼类物种和功能多样性的影响.发现洪枯水位变化仅对物种多样性指数中的物种数（Richness）产生显著差异，而对功能多样性的3个指数（功能丰富度指数（FRic）、功能离散指数（FDiv）和功能分散指数（FDis））均有显著影响.洪水期鱼类的Richness、FRic、FDiv和FDis指数均显著高于枯水期.同时，静水生境条件下的FRic指数要显著高于流水生境.本研究发现，与传统的物种多样性相比，基于功能性状的功能多样性对水位的洪枯变动更为敏感，河流周期性洪泛是泛滥平原生态系统中鱼类功能补充的重要方式.;Water level fluctuations between wet and dry seasons, assisting by lateral connectivity, play a fundamental role in underpinning the composition and distribution of fish fauna in floodplain lakes. The ecotone floodplains between the floodplain rivers and lakes are generally considered as the key areas where witness the exchange of fish species and the variations of biodiversity. However, the study of changes in taxonomic and functional diversity of fish communities in the ecotone floodplain in response to water level fluctuations is limited. Here we address this issue by measuring temporal (dry and wet seasons) and spatial (lotic and lentic habitat patches) changes in taxonomic and functional diversity of fish communities in the ecotone floodplain between the Yangtze River and Lake Caizi. A total of 52 species belonging to 37 genera, 12 families and 6 orders were collected in our study. Among them, there were significant differences in species number between wet and dry seasons, with 50 species and 42 species collected respectively. On the other hand, there was no significant difference in the number of species between lentic and lotic habitat patches, with 47 species and 48 species collected respectively. In comparison with wet season, the species richness, weight, abundance and importance value percentage of riverine species decreased by 7.3%, 6.3%, 14.4% and 12.0% in dry season. In comparison with lentic habitat patches, the species richness, weight, abundance and importance value percentage of riverine species increased by 5.3%, 14.6%, 18.0% and 22.3%. The fish fauna differences between seasons (dry and wet) and habitat patches (lentic and lotic) were determined by the abundance of Pseudorasbora parva, Saurogobio dabryi, Hemiculter leucisculus, Cyprinus carpio, Carassius auratus, Coilia brachygnathus, Pseudobrama simony, Culter ilishaeformis, Culter dabryi, Saurogobio gymnocheilus and Acheilognathus gracilis. Important value analysis showed that the dominant species of fish in lentic habitat patches and dry season were similar, and the dominant species of fish in lotic habitat patches and wet season were similar as well. The dominant species in wet season and lotic habitat patches were P. parva, S. dabryi, S. gymnocheilus and C. brachygnathus, while the dominant species in dry season and lentic habitat patches were C. carpio, C. auratus, H. leucisculus and P. simoni. Two-way ANOVA analysis indicated that one taxonomic diversity indices (Richness) and three functional diversity indices (FRic, FDiv and FDis) significantly differed between wet and dry seasons. Taxonomic richness, functional richness, functional divergence and functional dispersion were significantly higher in wet season than in dry season. Meanwhile, the functional richness was significantly higher in lentic than in lotic habitat patches. Functional diversity exhibited higher sensitivity than the traditional taxonomic diversity, since three functional diversity indices showed significant variations between wet and dry seasons. Meanwhile, our study highlight important functional recruitments of fish assemblages triggered by seasonal flood pulses.