Research On Community Assemblage Process And Mechanism Based On Niche-Neutral Continuum

For the past few years, the biodiversity problem has been received extensive attentions of the international community while community assembly as one of its main subjects, has also become a current research hotspot. The so-called community assembly is regarded as the mechanism of generating and maintaining species biodiversity. Many ubiquitous community patterns in nature, which could exhibit community structures, have already been noticed by ecologists, but different mechanisms were always uncovered behind the same pattern. A key challenge for ecologists is to identify which process mainly acting to produce the community patterns we see. And the topic of our dissertation is just chosen from this. In terms of above problems, a majority of community ecologists once argued between the processes dominant by traditional niche differentiation and the random processes which mainly generated under neutral hypothesis. After a lot of trying and experimental verifications, community ecologists are turning their attentions to the relative importance of multiple assemblage mechanisms rather than only focusing on a single leading process. Because the niche-neutral continuum could well present community dynamics under various niche and neutral combinations, all related contents in this dissertation will be expanded on the assumption.First, from the point of species abundance, the global and local abundance ranks on habitat gradient have been considered. We defined the abundance rank consistency of community and quantified it by indexes. This kind of pattern index has involved spatial factors and is able to express the spatial scale-dependent of abundance structure in community. Through mathematical simulation way, a spatially explicit niche-neutral continuum model was established. And after simulating community dynamic under several habitat structures, we found that, with a certain spatial structure of habitat resource, the abundance rank consistency index could be used to pinpoint the community assemblage position on niche-neutral continuum. Specifically, if habitat structure was clustering on some degree, a solely corresponding position on the niche-neutral continuum could be found by the same abundance rank consistency value. But for completely random habitats which rarely existed in reality, there were likely two different positions on continuum. What's more, as the included community sample process when calculating our consistency indexes, it is also necessary for us to analyze the contribution of sample design method, like sample number and window size. Our results showed that the effect of sample number to indexes Kendall rank-correlation and regression slope could be safely neglected but another index average variance was more sensitive to chosen sample numbers. If we considered future costing of field work and the quality of predicting result, Kendall rank-correlation and regression slope were also better than average variance.Additionally, since McGill et al. mentioned the plant community structure could be explained by functional trait, there were plenty of studies relating to this point. Ecologists always detected environmental filtering and niche differentiation processes by analyzing the trait dispersion patterns (like convergence or divergence) of plants. But only focusing on phenomenological trait-dispersion is not sufficient to uncover the community assemblage mechanism. Here we regarded the plant functional trait as one of niche function's input variables and also distinguished individuals in population. Our purpose is to explore which kind of assemblage community will be altered most by considering intra-specific variability. By focusing on the community placed on the niche-neutral continuum and after analyzing three kinds of popular community pattern indexes, we found that the community generated by large niche overlaps was more necessary for distinguishing individuals among the same population while for the community with completely niche differentiation, intra-specific difference could be safely omitted. In terms of the contribution of intra trait variance's magnitude, all the pattern indexes we considered, like species richness, rank-abundance curve and trait-abundance relationship, were not sensitive to the level of intra-specific variability but expecting the trait distribution figure. It has presented an exponentially changing tendency on the variance magnitude gradient.Generally speaking, we can calculate community's abundance rank consistency first, through which this community's mechanism position on niche-neutral continuum will be pinpointed. Then according to above conclusion, we could decide whether it is informative to record all individual's trait values when designing field studies.