TEMPORAL FLUCTUATIONS IN DEMOGRAPHIC PARAMETERS AND THE GENETIC VARIANCE AMONG POPULATIONS.

Contrary to assumptions commonly made in the study of population genetics, the demographic properties of many populations are not always constant. Important characteristics of populations such as migration rate and population size may vary in time and space. Moreover, local populations often come and go; the rate of extinction and the properties of colonization may also vary. In this paper, the approach to equilibrium following a disturbance in the genetic variance among populations is described. The rate of migration is shown to be critical in determining the extent to which extinction and recolonization affects genetic differentiation. Perturbations and variations through time and space in demographic parameters such as population size and migration rate are shown to be important in determining the partitioning of genetic variance. Equations are given to predict the average through time of genetic differentiation among populations in the event of a single disturbance or in constant fluctuations in the pertinent demographic parameters. In general, these fluctuations increase the FST of a species. Spatial demographic variation affects FST much more than temporal variation. These demographic properties make some species unsuitable for the empirical analysis of migration with indirect genetic measures. Demographic instability may play a large role in the evolution of genetic variation. © 1992 The Society for the Study of Evolution.