The Importance Of Niche Difierentiation For The Maintenance Of Species Diversity

The mechanisms of species coexistence and community assembly have long been core issues in community ecology. Niche theory and neutral theory are two major frameworks aiming at explaining patterns of biodiversity observed in nature. Niche theory emphasizes that local deterministic processes play a key role in species coexistence and community assembly. On the contrary, neutral theory emphasizes the importance of stochastic processes. The controversy about the relative importance of deterministic vs. stochastic processes in community assembly has been lasted for more than one century. However, no consistent conclusion has yet been reached. Now, ecologists are trying to integrate niche theory and neutral theory to explain the biodiversity patterns in real communities. As a starting point, the present paper mainly addressing the role of niche differentiation on species coexistence and community assembly by combining mathematical modeling, computer simulation and fitting the models to the observed data. On the one hand, we explore the effect of niche differentiation for species coexistence at large scales; on the other hand, by introducing niche differentiation into a neutral model for discrete local communities, we assess the predictive power of the hybrid niche-neutral models in coral reefs.The main results are as follows:1. The missing of niche differentiation will result in competitive exclusion and the system will reach a globally stable equilibrium soon. That is, the species with higher competitive abilities will displace all the rest species, and the equilibrium is globally sable, which implies that, without niche differentiation, whatever the initial proportion of each species is (except0), the system will eventually reach the equilibrium. Recruitment limitation and dispersal limitation can offset competitive exclusion at some extent, but the effect compared to Hurtt and Pacala’s model (1995) is rather limited. Actually, strong recruitment limitation and dispersal limitation is needed to offset competitive exclusion caused by very slight difference in the competitive ability among different species.2. When strong niche structure is incorporated into the multiple discrete communities’neutral model, the predicted patterns of species abundance distribution remain unchanged. When more complex niche differentiation are taken into account, that is, the per capita lifetime reproductive success and immigration of each species are identical in the same local community but they may differ in different local communities, the hybrid niche-neutral models fit the data of species abundance distribution and individual abundance distribution in spatially discrete communities much better than the pure neutral model. Indeed, neutral theory fails to predict the species number and individual number of common species. Individual-based IADs provide a more powerful test of model fit than the species-based SADs when the least square method is used for model fitting. According to the fitting results of hybrid models of more than two niches, there is a negative relationship between the predicted values of x and γ for different niches.According to the above results, we can conclude that niche differentiation is important for species coexistence at even large scales, and incorporating niche structure into the multiple discrete communities’ neutral model can greatly improve its predictive ability of models in coral reefs communities. Thus, niche differentiation plays very important roles in species coexistence and community assembly. Besides, we propose that it is necessary and feasible to integrate niche theory and neutral theory to explain patterns of species diversity in real communities.