Print PageOne of the most important issues in biogeography is to understand species' range limits. It has been suggested that because of less suitable conditions peripheral populations are smaller, less dense, more isolated and produce less seeds than central populations. As a consequence they should exhibit lower genetic diversity and greater genetic differentiation than central populations. We compared population characteristics and individual reproduction as well as genetic diversity and genetic differentiation of populations of the perennial, insect-pollinated rock plant Carduus defloratus (Asteraceae) along a gradient from the center to the margin of its distribution in Central Europe.
Results/Conclusions
As expected, peripheral populations were smaller, less dense and produced less viable seeds than central populations. Amplified fragment length polymorphism analysis indicated that genetic diversity was lower in peripheral than in central populations. However, the genetic distance between peripheral was lower than between central populations. The pairwise genetic distance between populations increased with their geographic distance. There was significant genetic differentiation between the two types of populations, but variation among populations within types was higher, and most of the genetic variation was among individuals within populations. In C. defloratus, the range limit may be influenced by the reduced reproductive success of peripheral populations. Seed abortion was higher in peripheral than in central population and increased with decreasing genetic diversity, indicating early inbreeding depression.
