Plant genetic diversity and population differentiation in the fragmented alpine landscape

Even though the alpine landscape is naturally fragmented and vegetative reproduction
is important in Geum reptans, I conclude that gene flow and repeated seedling recruitment
during succession might be more frequent than commonly suggested and is similar at different
altitudes. Random genetic drift plays an important role in population differentiation and is
suggested to account for the high variation in growth and reproduction among populations.
Gene flow may additionally counteract selective forces in alpine plants from contrasting
habitats: plants performed similar in most traits within the same environmental treatment
irrespective of origin. This indicates limited adaptation to different habitats and a high
phenotypic plasticity in G. reptans. Despite of the overall low competition strength and
susceptibility to warm temperature, great size-dependent plasticity in the proportion of sexual
vs. clonal reproduction ensures population peristence and reproduction in a lrage range of
habitat conditions.
Selection for larger seeds along the altitudinal trajectory can be confirmed in a majority
of alpine species, but is not generally operating. My results suggest that seed weight only
rarely changes as a single trait, but rather evolves as an element of a correlated set of
characters involving taxonomic differentiation at the species or at least infra-specific level.
In contrary to the findings with G. reptans in the naturally fragmented alpine
landscape, Scabiosa columbaria from recently created habitat remnants is affected by habitat
fragmentation more severely. Local extinction risk of S. columbaria is suggested to be
increased as a consequence of a decreased viability and of reduced phenotypic plasticity due to genetic erosion. However, there is only weak indirect evidence for a poorer plant performance
of small populations, indicating that population size is not always the best indicator for
population viability and genetic diversity. Restoration efforts should therefore not only tend
towards increasing local population sizes, but should also consider genetic diversity by itself
accounting for possible interactions between genetic and non-genetic effects on population
viability.
My results suggest, that plants from naturally fragmented habitats are clearly less
affected by isolation than plants in recently fragmented habitats. From the results with Geum
reptans it can be concluded that phenotypic plasticity may be a successful strategy to cope
with contrasting habitat conditions in the alpine landscape and probably also buffers against
possible effects of natural fragmentation.