Difference Among Species' Dispersal Ability And Species Coexistence

Species coexistence and biodiversity maintenance has been a hot topic in ecology. Species dispersal can have important effects on species distribution patterns, population dynamics, species' response to the environment factors and so on. It can also affect community structure and community dynamics. At present, community ecology theories including niche theory, neutral theory, neutral-niche continuity hypothesis, the stochastic niche theory hypothesis have all approved the role of dispersal and random processes on the community assembly. Plant diffusion process also plays an important role in restoration ecology, invasion biology and conservation biology.In this thesis, I choose the Clark2Dt model to analyze the influence of scale parameter u and shape parameter p on species coexistence. The relationship between species'dispersal ability and species coexistence time and species spatial distribution pattern were studied through simulation. All simulations were done under the initial completely random distribution and with the zero-sum assumption. I have shown that:1) When two species have the same dispersal ability and the same per capita fecundity, species coexistence time increases with species fecundity.2) When the two species have different dispersal ability but share the same per capita fecundity of one seed per generation, the coexistence times are almost the same with that predicted under neutral assumption. In this case, the effects of differences in dispersal ability are masked by the effects of random drift. When they both produce enough offspring, the coexistence time do not change with increased fecundity. That is to say, different dispersal ability can remove the effects of fecundity on coexistence time.3) When two species have different dispersal ability but the same per capita fecundity, long-distance dispersal species has an absolute competitive advantage and eliminate short-distance dispersal one.I have also studied the role of Allee effect in community ecology and conservation ecology. The results indicate that:1) When two species have the same dispersal ability and the same per capita fecundity, Allee effect significantly reduces two species coexistence time.2) When a certain intensity of Allee effect exists and two species have the same per capita fecundity, dispersal asymmetry can raise species abundance, which demonstrates the role of Allee effect and dispersal asymmetry on species coexistence. There is a threshold value of Allee effect to affect the coexistence of species. When Allee effect is very strong, both species tend to die whether they have the same dispersal ability or not.