The significance of genetic erosion in the process of extinction:I. Genetic differentiation in <i>Salvia pratensis</i> and <i>Scabiosa columbaria</i> in relation to population size

As part of a programme to determine the importance of the loss of genetic variation for the probability of population extinction, the amount of allozyme variation was determined in 14 populations of Salvia pratensis and in 12 populations of Scabiosa columbaria. Significant correlations were found between population size and the proportion of polymorphic loci (Salvia: r = 0.619; Scabiosa: r = 0.713) and between population size and mean observed number of alleles per locus (Salvia: r = 0.540; Scabiosa: r = 0.819). Genetic differentiation was substantially larger among small populations than among large populations: in Salvia G(ST) was 0.181 and 0.115, respectively, and in Scabiosa 0.236 and 0.101, respectively. The results are discussed in relation to genetic drift, inbreeding and restricted gene flow.