A Study On The Impact Of Urbanization On Stream Benthic Taxonomic Diversity And Functional Diversity

Being different from traditional taxonomic diversity, functional diversity is based on functional traits and consider the distribution of species traits among different communities. Using multiple traits to describe different ecosystem’s function, it can connect organisms to ecosystems, and reflect the ecosystem processes. But because there are many obstacles in its study, in our country, the relative study is only carried out in the field of terrestrial plant, in aquatic ecology is still in blank.Our study aims to investigate the response of aquatic insect community’s biological traits and functional diversity to land use change in the middle section of the Qiantang River Basin, Zhejiang Province. We sampled80sites, used continuous and binary functional traits, took quantitative and qualitative quantization means, respectively, to build two different species-trait data which we used to calculate functional index, then we compare and explain the variation of biological traits composition and functional diversity index by urbanization in aquatic insect communities.We chose11continuous biological traits to reflect aquatic insects’life history, resistance, physiological, etc. Using "fuzzy code" to quantify the traits, we applied fourth-corner statistic method to relate trait affinity, taxa abundance and environmental factor simultaneously and tested the significance of their relationships, hoping to find out the relationship between functional diversity and habitat change as well as biological community variation caused by human activity, in the further step. Our research found that stream habitat quality dramatically declined with the reduction of forest area in watersheds caused by human activities’land using, which also caused biological community variation. Consequently, some biological traits changes were detected as expected:the maximal body length decreased, the respiration patterns evolved from gills to tegument breathing, and the burrower’s abundance increased significantly. Functional diversity (Rao’s quadratic entropy) in reference sites was significantly higher than that in disturbed sites (P<0.001).We also chose8binary functional traits, reflecting insects’feeding habits, physiological characteristics, etc. Using "1-0" stands for presence/absence, we quantified the traits’information qualitative. Then calculated the traits’frequency and functional diversity index and compared the difference between reference sites and disturbed sites. We found that in disturbed stream, predator gradually disappeared; organism movement and the ability to disperse generally poor while burrowing capacity and tolerance became strong; breathing patterns turned to integumentary when dissolved oxygen declined; Feeding habits centered to collector-gatherers; rheophily trend to depositional, the degree of heterogeneity became lower. Most functional diversity index decreased significantly, which means when species richness decreased, the number of niche organism occupied decreased.Compared disturbed streams with reference streams, predator gradually disappeared; breathing patterns changed to the body wall of the main breathing with dissolved oxygen declined; trophic groups changed single, mainly to collector; dependent on the type of sediment heterogeneity decreased, mainly sedimentary. The majority of functional diversity index decreased significantly, reflecting the richness and the number of biological niche occupied was declining. Pearson correlation test verified the functional diversity index represented the three different aspects of the functional space, these three categories are independent of each other. Therefore, the fall of functional diversity index in different categories indicated the whole functional diversity decline.These results demonstrate that human-caused land use change resulting in stream water quality and habitat degradation which caused the variation of the species in community and a filtration of biological traits, eventually leading to changes in community functional diversity of aquatic insects. Biological traits and functional diversity are potential indicators to evaluate the ecological health in the future.