Gause and the Principle of Competitive Exclusion

Niche Overlap

In a revealing experiment, Gause challenged Paramaecium caudatum- the defeated species in his earlier experiments with a third species, P. bursaria. Because he expected these two species to also compete for the limited bacterial food supply, Gause thought one would win out, as had happened in his previous experiments. but that's not what happened. instead. bothh species survived in the culture tubes; the paramecia found a way to divide the food resources. how did they do it? in the upper part of the culture tubes where the oxygen concentration and bacterial density were high, P. caudatum dominated because it was better able to food on bacteria. however, in the lower part of the tubes, the lower oxygen concentration favored the growth of a difference potential food, yeast and P. bursaria was better able to eat this food. the fundamental niche of each species was only a portion of the tube. because of the niches of the two species did not overlap too much, both species were able to survive. however, competition did have a negative effect on the participants. when grown without a competitor, both species reached densities three times greater than they were grown eith a competitive

Competitive Exclusion

Gause's principle of competitive exclusion can be restated to say that no two species can occupy the same niche indefinitely when resources are limiting. certainly species can and do coexist while competing for some of the some resources. nevertheless, Gause's theory predicts that when two species coexist on a long term basis, either resources must not be limited or their niches will always differ in one or more features; otherwise, one species will outcompete the other and the extinction of the second species jwill inevitably result, a process refereed to as competitive exclusion