The Research Of Spatial And Temporal Patterns In Fish Assemblages During The Qingyi Watershed

To identify and explain how the distributions and abundance of stream fishes vary spatially and temporally is one of the themes of stream ecology. Revealing the spatial and temporal patterns in fish assemblages at multiple scales, identifying the necessary habitat for the survival and reproduction of stream fishes, and evaluating the influence of ecological environment on fish assemblages not only are the basis for the protection of species diversity and the reasonable exploitation of fishery resources, but also will contribute to the scientific management of stream ecosystems. In this study, using species composition and their abundance to describe assemblage structure, the spatial and temporal patterns in fish assemblages within the Qingyi watershed were examined to assess the influence of stream longitudinal gradient and network ecosystem on fish assemblages. In addition, the causing mechanisms of the spatial and temporal patterns in fish assemblages were explained with the relations between fish and different environment factors. The main results were as follows:1. Spatio-temporal patterns in fish assemblages along the longitudinal gradient of the Qingyi Stream.During April, July, October 2009 and January 2010, a total of 15 sites, representing 1st-5rd stream orders and 2 longitudinal gradients, were sampled, respectively. All specimens, amounting to 13, 647 individuals, represented 57 species (including Ctenogobius sp.), 15 families, and 5 orders. Cyprinidae fishes comprised on average 59.6% of total species richness. Species richness per sample amounted to 11.9±6.6 species, and abundance per site 227.6±205.5 specimens. Based on three-way ANOVA, fish species richness significantly varied among different stream orders and longitudinal gradients (P < 0.05). Species richness increased with the increase in stream order, and were more within the longitudinal gradient without the large dam than that disrupted by the dam. But no significant difference was observed in species richness among seasons (P > 0.05). According to ANOSIM and NMS, fish assemblages also presented significant spatial variation among stream orders and longitudinal gradients (P < 0.05), but not among seasons (P > 0.05). The result of SIMPER analysis show that the spatial variation in the abundance of Cobitis rarus,Parabotia fasciata,Rhodeus ocellatus and Sarcocheilichthys nigripinnis contributed most to the spatial pattern in fish assemblages. Based on CCA, fish assemblages were identified to be determined by some local habitat environment, such as elevation, substrate, water depth, current discharge, wetted width, and conductivity. Our result suggested that the ecological effects of a large dam have the nature of localization, because significant variations in assemblages between-gradient only occurred in 4th-order, not lower-order, streams.2. Spatial pattern in fish assemblages within the stream network ecosystem of the Qingyi Stream.The influences of local habitat and stream spatial positon on fish assemblages were examined from 1st-order through 3rd-order within on the Qingyi Stream in October 2009. A total of 9, 875 fish were captured throughout this study area, representing 36 species (including Ctenogobius sp.), 11 families, and 4 orders. Based on linear regression models, the most important environmental variables influencing fish species richness were water temperature and wetted width, but stream spatial position variables were less important. Using CCA, five environmental variables were identified to significantly in?uence fish assemblages, including three habitats (elevation, substrate and water depth) and two spatial variables (C-link and Link). Our results suggest that, in a heavily dammed watershed, by blocking the migration routes of fishes, dams weaken the in?uence of stream spatial position on fish species richness. However, fish species compositions are significantly in?uenced by both local habitat environment and stream spatial position, which is perhaps owing to the distribution of fish species according to ecological requirements not related to spatial processes.