Hierarchical Structures In Competitive PlantCommunities

Abstract

To explore how a stable size hierarchical structure may emerge in plant communities, a simple competition model for plant individuals with two types of competition mode, asymmetric and symmetric, is studied numerically and theoretically. The model incorporates size-ratio dependent interactions between individuals, which reflects the sensitivity of resource gain to differences in individual biomass at the seedling stage. From numerical simulations, the stability of the multi-layered size structure is determined by the relationships between the number of population, the degree of competitive asymmetry and the potential maximum relative growth rate (i.e. seedling's relative growth rate) as follows: (1) As the number of population and/or the degree of competitive asymmetry increases [decreases], multi-layered [mono-layered] size structure becomes stable; (2) As the potential maximum relative growth rate increases, the domain of stable mono-layered [multilayered] size structure becomes larger [smaller] . It is further shown that, when the potential maximum relative growth rate is fixed, (3) mult ilayered size structure is more likely to be stable under asymmetric competition than under symmetric competition; (4) mono-layered size structure is more likely to be stable under symmetric competition than under asymmetric competition. When the hierarchical structures are self-organized by the dynamic instability of the homogeneous state due to nonlinearity of competition, it is proved by theoretical analysis that these states are always locally stable. This is also suggestive of the mechanisms of species coexistence in plant communities. Transactions on Ecology and the Environment vol 27 © 1999 WIT Press, www.witpress.com, ISSN 1743-3541 26 Ecosystems and Sustainable Development