Effect of a predator on species diversity : a study under conditions of continuous cultivation

A study was made of the food web formed from a protozcan, Teterhymena pyriformis, two bacteria. Pseudomonas fluorescens and Escherichia coli, and a glucose minimal medium in chemostat culture. An attempt was made to further substantiate the idea that species diversity within a community can be dependent upon predation. The system was divided into simpler parts, first by demonstrating that each bacterial species in pure culture would achieve steady-state growth on the substrate, whereas the protozoa could not. In batch and steady-state growth studies of pure culture of the two bacterial species, P. fluorescens was the more successful. In competition studies between P fluorescens and E. coli in the chemostat. P. fluorescens population level was 100-to 1000-fold greater. Interestingly, E. coli’s steady-state population increased approximately 50-fold when P. fluorescens was added. (See more in text.)