Longitudinal Pattern And Formation Mechanism.in ? And ? Diversity Of Taxonomic And Functional Of Stream Fish Assemblages In The Xin'an River

Determining the spatial and temporal pattern of fish diversity in streams is a central issue in the development of fish ecology and can provide a scientific basis for the conservation and management of fish diversity.The longitudinal pattern of stream fish assemblages along the upstream-downstream gradient is recognized as a typically spatial heterogeneity of fishes.Although the longitudinal gradient pattern of the structure and diversity of taxonomic has been reported extensively and some general rules have been established,the functional structure and diversity based on the biological characteristics of fishes have received less attention,especially the connection with the environment and strategies for dealing with environmental changes.In this study,based on the fishes and environmental data collected from Xin`an River during May and November 2017.We have identified the changes in environmental factors such as local habitat variables,land landscape variables,and tributary spatial along longitudinal gradients,and the variations in the taxonomic and functional structure of fish assemblages and the distribution of taxonomic and functional?/?diversity along longitudinal gradients.Our results had as follows:?1?Along the longitudinal gradient of“upstream-downstream”,there were significant positive correlations between environmental factors such as water temperature,water width,water depth,stream order,D-link,urbanization area,agriculture area,and the distance from headwater;however,there were significant negative correlations between environmental factors such as current velocity,C-link,forest area and the distance form headwater.According to the feeding habits and functional morphological traits,all 45 species collected were divided into 16combined groups.Two-way crossed ANOSIM showed that both the taxonomic and functional organizations varied significantly across 1st-to 5th-order streams,but did not present significant among-season variation.Along the longitudinal gradient,hydrophilic species such as Phoxinus oxycephalus,Onychostoma barbatulum,Vanmanenia stenosoma have gradually decreased,and Ophiocephalus argus,Culter alburnus,Pelteobagrus fulvidraco have gradually increased.Both the taxonomic group and the functional organization structure of fish have affected by the combination of habitat variables,landscape variables,and tributary spatial.The tributary spatial location is more important.?2?Based on fish locomotion,feeding,habitat use,and position in the water column,functional richness?FRic?,functional evenness?FEve?,and functional dispersion?FDiv?were calculated,combining taxonomic alpha diversity of fish species such as Margalef,Shannon-Wiener,and Pielou,we have found that the FRic,FDiv,Margalef and Shannon-Wiener indices all changed significantly with the stream orders,but there was no significant change between seasons.On the contrary,both FEve and Pielou changed significantly with the season,but there was no significant difference between the stream orders.The Margalef index,Shannon-Wiener index,and FRic have a significant quadratic relationship with the distance form headwater,and FDiv shows a significant positive linear correlation.The alpha and beta diversity of fishes on the Xin'an River have affected by the combination of habitat environment,land landscape,and tributary spatial location.However,the spatial location of tributaries has the dominant factor influencing the diversity of taxonomic,while the diversity of functional has mainly affected by Land landscape variable effects.?3?The spatial variation in the taxonomic?diversity was mainly driven by species turnover,but variation in the functional?diversity driven by function nestedness and turnover.The?diversity of taxonomic and functional has varied significantly with the stream orders,and both had no significant relationship with seasonal changes.The?_s?r?r of taxonomic and functional has a significant binomial relationship with the distance from the headwater,showing a“?”distribution.The taxonomic turnover(Tax_sim)and functional nestedness(Fun_nes)have increased significantly with distance,while the taxonomic nestedness(Tax_nes)and functional turnover(Fun_nes)have decreased.The?diversity of taxonomic had influenced by the tributary spatial location and terrestrial landscape variables,while the functional?diversity had mainly affected by the land landscape variables.The results has indicated that the spatial and temporal distribution pattern of the taxonomic and functional structure and?and?diversity are different under the longitudinal gradient of“upstream-downstream”,and the?diversity has mainly caused by species turnover and diversity of functions?has caused by the combination of functional nestedness and turnover.The driving mechanism of the two spatial changes is different.In relation to the environment,the variables of spatial tributary location and local habitat mainly affect taxonomic organization,and land landscape variables mainly affect functional organization.