Community Assembly:an Insight From Soil Resources And Species Abundance In The Alpine

Mechanisms of biodiversity maintenance and community assembly are among the most important issues in the contemporary ecological research. Debates on this issue dates back to the beginning of the twenty century with the emergence of individualistic versus holistic concepts. In fact, both theories emphasized different aspects of community assembly. Accordingly, there are two types of theories explaining species coexistence. Classical niche theory asserts that species can coexist through niche differentiation incurred by competitive exclusion. However, niche theory fails to account for species coexistence in some communities of especially very high diversity. In contrast, neutral theory developed by Hubbell (2001) assumes that species share the same rate of birth, mortality and migration, and biodiversity can be maintained by stochastic birth, death and immigration in a local community. Neutral theory emphasizes the effects of stochasticity in community assembly, which is largely neglected by niche theory. However, neutral theory also received much criticism because of its equivalence assumption. In this paper, based on the dichotomy of plant community assembly, we study species diversity and community structure by investigating the relationship between soil resources and species abundance in the alpine meadow of Qinghai-Tibet plateau. The main results are as follows:1. The differences in soil recourses ratios result in dissimilarity of species composition in plant communities in heterogeneous habitat, and the abundance of dominant species are related to the soil recourses. In other word, habitat filtering plays an important role in regulating community species composition and relative abundance distribution.2. Dominant species almost use the same recourses without niche differentiation. Dominant species use the same recourses are not appearing competitive exclusion. Resource ratio hypothesis cannot account for species abundance distributions along gradients of resources.3. The relative abundance distribution of dominant species relate with soil recourses. The distribution tends to aggregative around favorable resources at the same recourse level. Neutral theory, which ignores the impact of environmental conditions for plant community assembly at local and met community scale, also fails to account for this pattern.4. Our results partially give supports for the stochastic niche theory. In study, species、abundance and biomass of dominant species have the simile tendency in a fit soil resource gradient. Under the interaction of environmental filters and organisms, dominant species occupy the favorable recourse region in the community, while the other species colonize successfully the rest of the region by stochasticity, and maintain high diversity in an alpine plant community.