THE POPULATION-GENETICS OF THE SELF-INCOMPATIBILITY POLYMORPHISM IN PAPAVER RHOEAS .11. THE EFFECTS OF LIMITED POLLEN AND SEED DISPERSAL, OVERLAPPING GENERATIONS AND VARIATION IN PLANT SIZE ON THE VARIANCE OF S-ALLELE FREQUENCIES IN POPULATIONS AT EQUILIBRIUM

The effects of limited pollen and seed dispersal, of overlap between g enerations and of variation in plant size on the steady-state variance of S-allele frequencies have been investigated in a simulated populat ion of size 3840 containing 16 S-alleles whose initial frequencies wer e exactly equal. Simulations were run with each of the 16 possible com binations of these four factors to investigate their effects on the ti me for the population to reach steady state and on the average varianc e of S-allele frequencies in steady state. The time to steady state ap peared to be relatively unaffected by any of the factors and was about 50 generations. However, the steady-state variance was markedly affec ted, with variation in plant size increasing this variance by an avera ge of 228 per cent and overlapping generations decreasing the variance by an average of 30 per cent. The effects of limited pollen and seed dispersal were individually small, although their combined effect was to increase the steady-state variance by an average of 12 per cent. Li mited seed and pollen dispersal, when combined with variation in plant size, caused the alleles to cluster. The four factors together caused a large increase in the average steady-state variance. Furthermore, e ven when a population is in steady state, the variance for a particula r generation can be considerably greater than this average value. Cons equently the frequencies of the S-alleles of a population in steady st ate can be very different. It is possible, therefore, that the large v ariation in S-allele frequencies found in samples taken from Papaver r hoeas populations is consistent with their being in steady state.