Density-dependent selection at high food levels leads to the evolution of persistence but not constancy in Drosophila melanogaster populations

Abstract

Mechanisms through which population dynamics evolve to be stable have been a subject of considerable interest in population biology. One of the ways through which population stability is likely to evolve is via density-dependent selection with or without an r and K trade-off. In this paper, we test whether the specific combination of egg number and food amount under which density-dependent selection is implemented affects the evolution of population stability attributes in D. melanogaster populations that have evolved under density-dependent selection for 75 generations. Our findings show that these populations have evolved higher persistence stability than controls, although constancy stability did not evolve. Moreover, these populations did not show an r-K trade-off, and evolved persistence largely through a significant decrease in sensitivity of growth rate to population density, especially at densities ranging from medium to the equilibrium population size. Qualitative comparison of these findings with those from another set of crowding-adapted D. melanogaster populations that had evolved both constancy and persistence stability, suggests that the ecology of larval crowding influences the consequent evolution of stability attributes. We discuss previous findings on the evolution of life-history traits to argue that differences in the ecology of density-dependent selection experienced at the larval stage affects population stability differently by altering the sensitivity of population growth rate to population density.