Survival in the alpine landscape : genetic, demographic and reproductive strategies of the rare monocarpic perennial "Campanula thyrsoides" in the Swiss Alps

Campanula thyrsoides is one of the few monocarpic perennials in the Swiss
Alps. Genetic connectivity among populations of this species is impeded due to the
heterogeneity of the alpine environment and consequently, a significant pattern of
decreasing population relatedness with increasing geographic distance can be found.
The comparison with two other alpine species studied at the same spatial scale showed
that the potential for long-distance seed dispersal does not necessarily translate into
increased population similarity. The results further suggest that other life-history traits,
especially the breeding system, may play an important role in genetic diversity
partitioning. These findings corresponds well with the current knowledge about
determinants of genetic diversity in plant populations. The molecular study also
corroborates the theory on glacial refugia in the European Alps by delimiting two
prominent areas of post-glacial plant migration. A very comforting result is the high
amount of genetic diversity that can be found even in small populations such that the
short-term adaptive potential of Campanula thyrsoides is assured.
Demographic analysis of two populations revealed that survival and growth are
the most important determinants of population persistence. C. thyrsoides seems to
follow an evolutionary stable flowering strategy which is characterized by an optimal
size-dependent flowering threshold. Age at reproduction varied largely in this species
and such a pronounced generation overlap efficiently buffers environmental variability.
Simulation approaches further showed that C. thyrsoides is most likely micrositelimited
and consequently has a large potential for population growth. In general, this
study confirms the findings of similar investigations and the novel combination of
methods applied have proven powerful to study in depth the important demographic
parameters of a long-lived alpine plant, potentially facilitating future research.
The pollination experiment established firm proof for an obligatory outcrossing
breeding system in C. thyrsoides which does not break down as flowers age. The study
also demonstrated the minimal risk of population decline as a result of inbreeding
depression.
From the three studies summarized above and the information accumulated in
the general life-history analysis I conclude that C. thyrsoides is well adapted to the
variability of the alpine environment, that the genetic and demographic requirements for
short-term adaptive capacity and long-term evolutionary potential of this species is
assured and that no specific conservation measures have to be taken for this naturally
rare species.