Figure 16.4 Competition between two species of protists. Gause raised different species of protists and measured the populations in terms of the total volume of cells in the container. When he raised each species separately on a fixed daily ration of bacteria, the population of (a) P. aurelia and (b) P. caudatum grew rapidly until they reached their carrying capacity. (c) When the two species were grown together, P. aurelia continued to grow well but P. caudatum was reduced to a very low population density. Because P. caudatum was still present in low numbers, P. aurelia did not attain the same population size as when it was raised alone.

Data from G. F. Gause, The Struggle for Existence (Williams & Wilkins, 1934).