A computer-simulation study of predator-prey relationships in a single-stage continuous-culture system

Abstract A mathematical model describing the growth of two microorganisms, one preying upon the other, in a completely-mixed single-stage continuous-culture reactor has been developed. In the simple food chain considered, it was assumed that a soluble nutrient was continuously supplied to a population of bacteria which in turn was utilized by a population of holozoic ciliated protozoa. The population dynamics of this model system were investigated by digital computer simulation. The results of an earlier experimental study on the ciliate Tetrahymena pyriformis and the bacterium Klebsiella aerogenes were used as a basis for the simulation studies. Limit-cycle (unstable focal point) oscillations of the three population variables, substrate, bacteria, and ciliates, were generally observed in simulation studies but at high dilution rates steady-state conditions were established. Steady-state values were approached either via damping oscillations (stable focal point) or via non-oscillatory variations (stable nodal point) whereby the populations asymptoted to steady-state values. The effects of the magnitude of the kinetic constants, the maximum specific growth rate, and the saturation coefficient, of both predator and prey, were investigated by computer simulation. The methods of prediction proposed by Canale (1969) were tested and confirmed by simulation techniques.