Composition Mechanism Of Fish Community Structure In Poyang Lake And Its Typical Tributaries

Poyang Lake is the largest freshwater lake in China,and it is also one of the only three lakes connecting the Yangtze River at present,which is rich in fishery resources.Over the years,the development and transformation of the Yangtze River and other tributaries of Poyang Lake have changed the ecological environment of the Poyang Lake basin,and the fishery resources of the region are bound to be affected.The study on the structure and construction mechanism of fish community in Poyang Lake region will provide a theoretical basis for the protection of fishery resources in Poyang Lake region and better carry out the protection of fishery resources.The construction mechanism of biological community has been generally accepted by ecologists as the result of random ecological drift(neutral theory)and niche differentiation(niche theory).Based on the survey data of fish resources in Poyang Lake and its tributaries in the summer of 2018,this paper analyzes the species composition and spatial structure of fish community in Poyang Lake basin.At the same time,combined with neutral theory and niche theory,the construction mechanism of fish community in Poyang Lake region was analyzed by means of phylogeny and stable isotopes.The main results are as follows:1.In the investigation of the summer fish resources in the Poyang Lake basin,the species composition of the Poyang Lake area is quite different from that of Xiushui.and the Poyang Lake area can be divided into the Northern group,the Southern group and the Eastern group.the species composition of the Northern group basically covers the species of the Southern group and the Eastern group,and the Northern group is connected with the Yangtze River,indicating that the species composition of the Poyang Lake area is mainly affected by the communication with the Yangtze River.2.The phylogenetic community structure on the sampling point scale in Poyang Lake and its tributaries was analyzed.Among the 24 sampling sites,the sampling sites with more special environment(such as the confluence of rivers and lakes and the confluence of tributaries)usually show aggregated community structure,and environmental filtration plays a leading role.In the sampling sites where the environment is less affected by water bodies such as other rivers,it usually shows a divergent community structure,and the competition mechanism plays a leading role.The results showed that the phylogenetic community structure of fish community was mainly affected by the environment of sampling sites.3.When the phylogenetic community structure of Xiushui in Poyang Lake and its tributaries was analyzed on a small regional scale,it was aggregated community structure in the areas with more special environment(Southern group),and environmental filtration played a leading role.In the areas where the environmental performance was less affected by other rivers and other water bodies(Northern group,Eastern group,Xiushui group),it showed divergent community structure,and the competition mechanism played a leading role.4.When the phylogenetic community structure of Xiushui in Poyang Lake and its tributaries was analyzed on a large regional scale,the lake group,as a whole with high spatial heterogeneity and large environmental capacity,showed divergent community structure,which was mainly affected by competition mechanism,while Xiushui group showed aggregated community structure,which was mainly affected by environmental filtration.5.By using the method of stable isotope analysis,the nutritional niches of 7 representative fish species in 4 sampling sites of Poyang Lake were compared and analyzed.It is found that different species have obvious differences in nutritional niche.The same species has different nutritional niches in different environments.The species competition relationship represented by the nutritional niche is generally consistent with the community construction mechanism of community phylogenetic analysis,that is,compared with the sites where environmental filtration dominates the community construction mechanism,at the sites where competition dominates the community construction mechanism,nutrition competition is more intense.