THE EFFECT OF DELAYED POPULATION-GROWTH ON THE GENETIC DIFFERENTIATION OF LOCAL-POPULATIONS SUBJECT TO FREQUENT EXTINCTIONS AND RECOLONIZATIONS

Investigated the effects of delayed population growth on the genetic d ifferentiation among populations subjected to local extinction and rec olonization, for two different migration functions; (1) a constant mig ration rate, and (2) a constant number of migrants. A delayed period o f population growth reduces the size of the newly founded populations for one or several generations. Whether this increases differentiation among local populations depends on the actual pattern of migration. W ith a constant migration rate, fewer migrants move into small populati ons than into large, thus providing ample opportunity for drift to act within a population. A prolonged period of population growth thus mak es the conditions for enhanced differentiation between local populatio ns less restrictive and also inflates the actual levels of differentia tion. The effect depends on the relative magnitudes of k(e), the effec tive number of colonizers and k, the actual number of colonizers. When there is a constant number of migrants into a population per generati on, migration into small populations is increased. This increase of mi gration in small populations counteracts the effects of genetic drift due to small population size. It increases the rate by which populatio ns approach equilibrium, as small populations are swamped by migrants from larger populations closer to genetic equilibrium, and overall lev els of differentiation are thus reduced. I also discuss situations for which the results of this paper are relevant.