Examination of a smallest CELSS (microcosm) through an individual-based model simulation.

Research of the effect of space environment on an ecosystem consisting of plants and animals is essential when they are to be positively used in space. Although there have been experiments on various organisms under space environment in the past, they mainly studied the effect of space environment on an individual organism or a single species. Microcosm is drawing attention as an experimental material of an ecosystem consisting of multiple species. The object in this research is to understand the nature of this network system called ecosystem. Thus, a mixed microorganism culturing system consisting of three types of microorganisms which form a minimum food chain system as a closed ecosystem (chlorella as the producer, bacteria as the decomposer, and rotifer as the consumer) was taken for the subject, on which to research the universal characteristics of ecosystems. From the results of experiments under the terrestrial environment, formation of colonies, which is an ecological structure, has been observed at its mature stage. The organisms form an optimal substance circulation system. Therefore, formation of colonies in simulation models is important. Many attempts have been made to create ecosystem models. For example, the Lotka-Volterra model forms a simultaneous equation with the differential equation expressing predator and prey relationship and many numerical calculations have been conducted on various ecosystems based on expanded L-V models. Conventionally, these top-down methods have been used. However, since this method only describes the average concentration of organisms that are distributed uniformly throughout the system and cannot express the spatial structure of the system, it was difficult to express ecosystem structures like colonies and density distributions. In actual ecosystems, there is heterogeneity in the number of individuals and in substance density, and this is thought to have great significance in ecosystems. Consequently, an individual-based model was used that applies rules to predator-prey relationship, suppression, production, self suppression, etc., of each species. It enabled the emergence of the overall system only by its local rules, and it was possible to reproduce colony generation. In addition, the transition and the ratio of populations for each species match well with experimental results.