What is the approximate carrying capacity of Paramecium aurelia cultured alone

The fourth example comes from the classic work of the great Russian ecologist G. F. Gause, who studied competition in laboratory experiments using three species of the protozoan Paramecium (Gause, 1934, 1935). All three species grew well alone, reaching stable carrying capacities in tubes of liquid medium. There, Paramecium consumed bacteria or yeast cells, which themselves lived on regularly replenished oatmeal (Figure 8.3a).

When Gause grew P. aurelia and P. caudatum together, P. caudatum always declined to the point of extinction, leaving P. aurelia as the victor (Figure 8.3b). P. caudatum would not normally have starved to death as quickly as it did, but Gause's experimental procedure involved the daily removal of 10% of the culture and animals. Thus, P. aurelia was successful in competition because near the point where its population size leveled off, it was still increasing by 10% per day (and able to counteract the enforced mortality), whilst P. caudatum was only increasing by 1.5% per day (Williamson, 1972).

By contrast, when P. caudatum and P. bursaria were grown together, neither species suffered a decline to the point of extinction - they coexisted. But, their stable densities were much lower than when grown alone (Figure 8.3c), indicating that they were in competition with one another (i.e. they 'suffered'). A closer

... between Paramecium species,...

Figure 8.3 Competition in Paramecium. (a) P. aurelia, P. caudatum and P. bursaria all establish populations when grown alone in culture medium. (b) When grown together, P. aurelia drives P. caudatum towards extinction. (c) When grown together, P. caudatum and P. bursaria coexist, although at lower densities than when alone. (After Clapham, 1973; from Gause, 1934.)

Figure 8.3 Competition in Paramecium. (a) P. aurelia, P. caudatum and P. bursaria all establish populations when grown alone in culture medium. (b) When grown together, P. aurelia drives P. caudatum towards extinction. (c) When grown together, P. caudatum and P. bursaria coexist, although at lower densities than when alone. (After Clapham, 1973; from Gause, 1934.)

look, however, revealed that although they lived together in the same tubes, they were, like Taniguchi and Nakano's fish and Connell's barnacles, spatially separated. P. caudatum tended to live and feed on the bacteria suspended in the medium, whilst P. bursaria was concentrated on the yeast cells at the bottom of the tubes.

Continue reading here: Competition between diatoms

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