Climatic oscillations and the fragmentation of plant populations - genetic diversity within and among populations of the glacial relict plants Saxifraga paniculata (Saxifragaceae) and Sesleria albicans (Poaceae) ; with 26 tables in the text and in the appendix

Saxifraga paniculata and Sesleria albicans are glacial relict plants. The present distribution of the two species is a result of the climatic changes after the last glaciation. Population size and range of Saxifraga and Sesleria were greatly reduced since the end of the pleistocene. Populations of Saxifraga and Sesleria were fragmented at least since the end of the last glaciation. Furthermore, the relict populations colonize habitats, which differ from each other with regard to ecological conditions. In the present investigation this was used to study the consequences of longterm isolation for the genetic diversity of plant populations and to analyze the genetic differentiation of populations and the development of ecotypes. The results clearly showed a high level of geographic differentiation among populations of Saxifraga paniculata and a significant correlation of the genetic distance and the geographic distance between the populations. In contrast, Sesleria albicans exhibited only a low level of geographic differentiation. A significant correlation of the genetic distance and the geographic distance could not be observed. Both S. paniculata and S. albicans exhibited considerable levels of genetic diversity within populations. However, genetic diversity was slightly higher within populations of Sesleria. Furthermore, genetic variability highly significant correlated with population size in both species. Peripheral relict populations of both species were genetically less variable than the populations from the present main distribution area in the Alps. Mutualities and differences between the two species can be explained by the history of the populations, the pollination system and distribution of the species. The results of this thesis show the significance of population genetic data for the formulation of appropriate management strategies.