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75. Computer Simulation of a Microorganic Ecology as a Self-sustaining System of Complexity
Masahiro Doi, Tetsuya Sakashita, Shoichi Fuma, Hiroshi Takeda, Kiriko Miyamoto and Yuji Nakamura
Keywords: aquatic microcosm, protozoa, bacteria, intraspecific, interspecific competition, interaction, feedback system, self-organization
Ecology is a nonlinear system of complexity structured by interactions among components and environment. Since very powerful mathematics and information tools are now available in terms of heuristic mathematical theory (e.g. cellular automata, genetic algorithm, etc.) and recent computer systems are highly sophisticated, it may be possible to describe how ecological systems and their components are likely to interact using computer simulation techniques by providing a simplified model on the basis of principles in the ecological systems, i.e., self-organization, feedback in response to disturbance, emergent behavior, diversity, etc.
This study explores a microorganic closed-ecosystem by computer simulation to illustrate symbiosis among populations in the microcosm that consists of the heterotroph protozoa, Tetrahymena thermophila B as a consumer, autotroph algae, Euglena gracilis Z as a primary producer and saprotroph Bacteria , Escherichia coli DH5, as a decomposer.
The simulation program is written as a procedure of StarLogoT, which was developed by the Center for Connected Learning and Computer-Based Modeling, Tufts University, which is a super set of StarLogo partly developed by the Media Laboratory, Massachusetts Institute of Technology. The virtual microcosm is structured and operated by the following rules.
1) Environment is defined as a lattice model, which consists of 10,201 square patches
2) Each patch has its own attributes, Nutrient, Detritus and absolute coordinates
3) Components of the species, Tetrahymena, Euglena and E. coli are defined as "turtles", and each turtle has its own attributes as X- and Y-coordinates, heading direction, age, life span potential, energy, breeding threshold, etc.
4) Each component of the species, Tetrahymena, Euglena and E. coli, lives its life by moving randomly, feeding (or consuming) a Nutrient from the "environment", and excreting its metabolic products to the "environment" as Detritus, breeds if it has more energy than the threshold and dies when its age reaches the life span potential if its energy is lost.
5) Only Euglena stores part of the sunlight energy as a potential food energy by photosynthesis process (biogeochemical Nutrient cycle), and E. coli breaks down the organic compounds of dead protoplasm or metabolic wastes (Detritus) and releases inorganic substances (Detritus food chain). A schematic figure of the Environment and species in the computer is illustrated in Fig. 25.
It was found that computer simulation is a valuable tool to illustrate symbiosis among populations in the microcosm, where a feedback mechanism acts in response to disturbances and interactions among species and Environment. In the simulation, the results of the population balance showed a probabilistic uncertainty and diversity, since some parameters, i.e., initial energy, initial age, life span potential and breeding energy threshold, etc, showed significant stochasticity. The selection pressure might be high in the first critical minutes of operation, which consists of both intraspecific and interspecific competitions. More computer-based simulation trials must be carried out.
Publications:
Fuma, S. et al. : Proceedings of the International Workshop on Comparative Evaluation of Health Effects of Environmental Toxicants Derived from Advanced Technologies, (Chiba, Japan), 131-144. 1998.
Kawabata, Z. et al. : J. Protozool. Research, 5, 23-26, 1995.
