Gene diversity and demographic turnover in central and peripheral populations of the perennial herb Gypsophila fastigiata

Within-population gene diversity (H-S) was estimated (using allozyme markers) for 16 populations of the perennial, outcrossing plant, Gypsophila fastigiata, on the Baltic island of Oland. The populations were characterized by data on extent, density, life-stages, and habitat diversity. Populations were classed as central or peripheral in relation to the distribution of ''alvar" (habitats with shallow, calcareous soils on limestone bedrock) on southern Oland. Three minimal adequate models were used to explain H-S and the proportions of juveniles and dead adults. In the first model, H-S was significantly lower in peripheral populations and there were no significant additional effects of other explanatory variables. The lower diversity in peripheral populations can be explained by a combination of genetic drift (in populations that vary in size in response to habitat fragmentation) and lower levels of interpopulation gene flow than in central populations. In the two life-stage models, peripheral populations had significantly larger proportions of both juveniles and dead adults indicating a greater demographic turnover than in the central populations. There were also significant effects of H-S and species diversity on the proportion of juveniles. The central or peripheral position of populations is the strop est predictor of both within-population gene diversity and life-stage dynamics in Oland G. fastigiata.