Responses Of Fish Assemblages And Diversities In Headwater Streams To The Urbanizations

Human activities may local habitat conditions,and alter fish assemblages and diversities in streams by the process of invasive species replacing indigenous species.Assessing the influences of anthropogenic disturbance on fish assemblages and diversities may provide scientific information on recovering,conserving and managingfish diversity.Although the effects of urbanization on biodiversities have been reported numerously,most studies focused on birds,plants,insects,and so on.However,the responses of fish assemblages and diversities in headwater streams to the urbanization have received less attention,especially for different species types?indigenous fishes and native-invasive fishes?and data types?species occurrence and abundance information?.Therefore,during the August and November in 2017,we surveyed 26 samples and set up two habitat types?i.e.,the urbanization and the free-slowing segment far away from the urbanization?in each sample to obtain the habitat and fish data from the first headwater streams located in the Xin'an River.We aimed to analyze 1)the effects of the urbanization on local habitats,fish community structures and patterns of the compositional distribution;2)the influences of the urbanization on alpha?i.e.,species richness and abundance?and beta?i.e.,compositional variation between-communities?diversity of fish assemblages based on different species categories and data types.Our main results were as follows:?1?Local habitat and fish assemblages:Although there was no significant variation of the habitat heterogeneity between the urbanization and free-flowing segments,the spatial heterogeneity of the former was slightly higher than the latter.The habitat heterogeneity in the wet season was lower than the dry season,which was consistent between the urbanization and free-flowing segments.Fish assemblage structures overlapped significantly between two habitats in the wet season.The significance depends primarily to abundance changing of some key species,such as Vanmanenia stenosoma,Cobitis rarus,Rhodeus ocellatus,Odontobutis potamophila,etc.We found the significant effects of local habitat variables?i.e.,conductivity,water temperature,pH and urbanization area?on fish assemblages.Fish assemblages in urbanization represented segregating patterns but that of free-flowing segments showed aggregating patterns.?2?Alpha and beta diversities:Compared with that in the free-flowing segments,species richness of the indigenous fishes significantly decreased but that of the native-invasive fishes increased in urbanizations.The alpha diversity was significantly correlated with the habitat variables,such as water depth and water wetted.Although most pairs of communities showed the same direction of changes for the occurrence-based and abundance-based similarities?i.e.,beta diversity?,some cases presented contrasting outcomes,i.e.,occurrence-based differentiation but abundance-based homogenization.Compared with the free-flowing segments,both beta diversities in urbanizations(?_sor and?_bc)increased significantly,which implied fish differentiation in urbanization.The patterns of community changing mainly contained“species turnover”and“balanced variation in abundance”when the?_sor and?_bcc were decomposed.For an example of fish data in August,the significant“distance decay of similarity”happened between beta diversity(?_bc,?_simim and?_bal)and distance of urbanization.Our results suggest the higher spatial heterogeneity in the urbanization resulted in the alpha diversity of indigenous fishes and native-invasive fishes decreased and increased respectively,and the beta diversity between-communities of all fishes increased.Furthermore,if we could not distinguish different species categories and data types,we may gain one-sided even incorrect results when assessing the responses of fish assemblages and diversities to anthropogenic disturbance.