The Growth of Mixed Populations of Chilomonas paramecium and Tetrahymena pyriformis

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Abstract
In mixed cultures where C. paramecium and T. pyriformis W were in competition for the same dissolved food, the population size of both spp. (expressed in terms of total number of organisms), as well as size and shape of individual organisms, were all affected by the presence of the other sp. Size of Chilomonas population was significantly larger in mixed than in single cultures up to the stationary phase, after which Chilomonas rapidly decreased in numbers and finally died out. Tetrahymena population was also larger in mixed cultures in early stages, though by the beginning of stationary phase this was not so. Only when Chilomonas had died out did Tetrahymena population again reach the size of that in single cultures. In terms of total volume of organisms, growth of Tetrahymena population was not as good initially as in single cultures. Later, when Chilomonas population became small, total volume of Tetrahymena population increased and finally reached population size in single cultures. C. paramecium and T. pyriformis were both more slender in mixed than in single cultures, differences being statistically significant. Variability of organisms was greater in mixed cultures and changed with age of population. During population growth, individual size of Chilomonas and Tetrahymena changed; but the time-course of change was different for 2 spp. While the size of Chilomonas increased in logarithmic phase and then decreased, the size of Tetrahymena decreased in logarithmic phase and increased in phase of negative growth acceleration. In old cultures, size of both spp. was smaller than at the beginning of the stationary phase.

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