On the Local Coexistence of Species in Plant Communities

Coexistence of many competitive species is very common in natural plant communities. For example, almost all forests and grasslands consist of various species. Extremely high biodiversity is seen in tropical rain forests. Grassland communities also often consist of many species. In plant communities, spatially competitive species of plants coexist in a mosaic pattern. Communities with a single species are very extremely rare in nature. However, mathematical studies show that the local coexistence of spatially competitive species is rarely achieved even with two competitive species. Many studies have introduced external factors to promote coexistence, such as immigration of seeds, seed dormancy, spatial heterogeneity and stochastic environments. Certainly coexistence is achieved under some circumstance in these models. However, we lack the evidence of such external factors in many plant communities. Natural coexistence of competitive species seems more prevailing than that expected from that with external reasoning. Therefore, it is reasonable to consider the possibility of internal factors promoting local coexistence of competitive species. Here we consider a plant community of two spatially competitive species in a lattice environment. We simulate the competitive interactions between the two species. Unlike the traditional models, we assume that the competition between the two species induces the replacement/takeover of one species by the other. This competitive superiority means that the reaction acts like predation in a mathematical context. We show that such replacement allows the local coexistence of two locally competitive species to some extent. Competitive interaction may take a various form of mathematical relations in spatially competitive communities. The rarity of coexistence in previous models may be the artefact of the Lotka-Volterra type competition.