The Impact Of Negative Density Dependence And Habitat Filtering On Biodiversity Of Seedlings In A Subtropical Forest

Negative density dependence and habitat filtering are important hypothesis to explain thecoexistence of species and the biodiversity of forest communities. Negative density dependenceassumes that-intraspecific competition of common species and interspecific competition amongclosely related species for similar vectors of resources, or negative interactions within species oramong closely related species by sharing similar pathogens and predators can provide space fornon-dominant species. Habitat filtering is the process that a particular habitat selects species withsimilar traits that can adapt to the habitat and eliminates other species. Previous studies focusedon testing the hypotheses of negative density dependence and habitat filtering by analyzing thespatial pattern of species diversity. Our study here attempted to test these two mechanisms to byanalyzing the temporal variation of community phylogenetic diversity and functional diversity.Recently, ecologists integrated evolutionary biology with community ecology and proposedcommunity phylogenetics. Phylogenetic relationship can be used to summarize the expectedsimilarity among species in traits under the hypothesis of niche conservatism. Phylogeneticdiversity combines biological diversity with the evolutionary relationship among species.Functional diversity combines biological diversity with functional traits of species in acommunity. Phylogenetic diversity and functional diversity will provide new insight for searchof mechanisms of community assembly.In this paper, we analyzed the seedlings dynamics (diameter <1cm) in a24ha-plot inGutianshan National Nature Reserve. Using seedlings dynamic data from2006to2007, weanalyzed the temporal change of spatial pattern of phylogenetic α diversity and β diversity ofseedlings in342plots located in two main habitats. We found that phylogenetic α diversity ofseedling in the same habitat increased significantly over time, suggesting that negative density dependence within plots may locally eliminate closely related species and increase phylogeneticα diversity. In contrast, phylogenetic β diversity of seedling in the same habitat declinedsignificantly over time, suggesting habitat filtering may homogenize the communities in aparticular habitat by selecting similar species that can tolerate the habitat. These resultscollectively suggested that: negative density dependent and habitat filtering work together tomaintain the diversity of communities in the subtropical forest.We also studied the impact of negative density dependence and habitat filtering on seedlings’functional diversity in Gutianshan plot. Five ecologically important functional traits of seedlings(DBH <1cm, height <80cm), i.e., wood density, stomatal density, specific leaf area, leaf nitrogencontent and leaf phosphorus content, were collected in2006and2007outside of Gutianshan24ha plot in Gutianshan Reserve. We analyzed the temporal change of functional diversity ofseedlings. We found that: functional α diversity of wood density, specific leaf area, leaf nitrogencontent and leaf phosphorus content except stomatial density increased significantly over time.Functional β diversity of wood density, stomatal density, specific leaf area and leaf phosphoruscontent except leaf nitrogen content measured by nearest taxa distance (Dnn) declined over timewhile functional β diversity measured by pairwise distance (Dpw) increased significantly. Theresults showed that negative density dependence can promote functional α diversity ofcommunities and habitats filtering can reduce the functional β diversity of communities of somefunctional traits within a habitat.