Computer Experiment on the Complex Behavior of a Two-Dimensional Cellular Automaton as a Phenomenological Model for an Ecosystem

Numerical studies are made on the complex behavior of a cellular automaton which serves as a phenomenological model for an ecosystem. The ecosystem is assumed to contain only three populations, i.e., a population of plants, of herbivores, and of carnivores. A two-dimensional region where organisms live is divided into square cells and the population density in each cell is regarded as a discrete variable. The influence of the physical environment and the interactions between organisms are reduced to a simple rule of cellular automaton evolution. It is found that the time dependent spatial distribution of organisms is, in general, very random and complex. However, under certain conditions, the self-organization of ordered patterns such as rotating spirals or concentric circles takes place. The relevance of the cellular automaton as a model for the ecosystem is discussed.