DENSITY-DEPENDENT NATURAL-SELECTION DOES NOT INCREASE EFFICIENCY

Populations of Drosophila melanogaster kept at high population density (K-selected) for 125 generations have higher larval viability than populations kept at low densities (r-selected) when both are raised under crowded conditions. In addition K-selected adults that emerge from crowded cultures are larger than their r-selected counterparts. These differences cannot be explained by differences in efficiency of food use. The minimum food required for successful pupation is actually greater in the K-selected populations. I conjecture that there may be a trade-off between minimum food requirements and competitive ability, which has changed substantially in the K-selected populations. The possibility that K-selected larvae can dig more more deeply and gain access to unused food is examined and rejected as a possible explanation of the viability differences. Evidence is provided supporting the hypothesis that the differences in viability may be due to an increased tendency of the K-selected larvae to pupate off the surface of the medium. © 1990 Chapman and Hall Ltd.