Evolution of competitive ability in Drosophila by density-dependent natural selection.

The theory of density-dependent natural selection predicts that populations kept at extreme densities should evolve different competitive abilities for limited resources. These predictions have been tested with laboratory populations of Drosophila melanogaster. Six independent populations were maintained in two environments, called r and K, for 128 generations. In the r environment, population sizes were small and resources for larvae and adults were abundant. In contrast the populations in the K environment were large and crowded, and resources, such as food and space, were in short supply. The relative competitive ability for food has been estimated for each population. Populations from the K environment consume food at a rate that is 58% greater than the average rate for the r population. The differentiation of competitive abilities in these populations is due to natural selection and is consistent with predictions from the theory of evolutionary ecology.