The Impacts Of Water Level Fluctuations Between Wet And Dry Seasons On Community Structure And Functional Diversity Of Fish Communities In The Ecotone Floodplain Of Lake Caizi

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.In this paper,the transition ecotone of Lake Caizi was selected as the research area.The temporal and spatial dynamic characteristics of the fish community structure in the transitional floodplain between the Yangtze River and Lake Caizi were analyzed through the systematic fish survey,and the taxonomic diversity and functional diversity of the fish community in the transitional ecotone were calculated respectively.The main findings are as follows:1.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.50 species and 42 species were collected respectively,while there was no significant difference in the number of species between lentic and lotic habitat patches,47 species and 48 species were collected respectively.Compared 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;compared 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%.Our results demonstrated that the spatial and temporal patterns of fish assemblages in the transitional floodplain between the Yangtze River and Lake Caizi were significantly affected by the changes of water levels and different environments.2.The fish fauna differences between seasons(dry and wet)and habitat patches(lentic and lotic)were determined by the abundance of Saurogobio dabryi,Hemiculter leucisculus,Saurogobio gymnocheilus,Cyprinus carpio and Carassius auratus.Important value analysis showed that the dominant species of fish in lentic habitat patches and dry season were similar,while the dominant species of fish in lotic habitat patches and wet season were similar.The dominant species in wet season and lotic habitat patches were Saurogobio dabryi,while Hemiculter leucisculus,Cyprinus carpio and Carassius auratus were dominant in dry season and lentic habitat patches.3.Two-way ANOVA analysis indicated that one of taxonomic diversity indices(richness)and three of 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(P<0.05).Meanwhile,the functional richness was significantly higher in lentic than in lotic habitat patches(P<0.05).Functional diversity exhibited higher sensitivity than the traditional taxonomic diversity,since three functional diversity indices showed significant variations between wet and dry seasons.4.Ward clustering method was used to classify functional groups based on 9 functional traits related to diet,body shape,ecological habits and life history characteristics of 52 species of fishes.The results showed that the functional groups G2,G9 and G10 was significantly higher in wet season(P<0.05);the abundance of functional groups G3 and G5 was significantly higher in lentic environments(P<0.05);and the abundance of functional groups G1 and G10 was significantly higher in lotic environments(P<0.05).5.Compared with taxonomic diversity,we detected higher sensitivity of functional group diversity,since three functional group diversity indices(functional group Richness;functional group's Shannon-Wiener and functional group's Simpson indices)were significantly higher in wet season(P<0.05).