Niche width and variation within and between populations in colonizing species (Carex flava group).

Taxa of the Carex flava group in Switzerland show a trend towards increased colonizing ability (r-selection). High colonizing ability is correlated with a large fundamental but a small and discontinuous realized niche. It is argued that r-selected species with wide niches should be monomorphic with generalists rather than polymorphic with specialists since they have small effective population sizes in which high genetic variability cannot be maintained. The most r-selected taxon of the group, C. viridula spp. viridula, has indeed the lowest genetic variability within populations but, in ecologically important characters, expresses the highest plasticity. The taxonomically important characters (inflorescences) have high heritability and differences between populations of C. viridula ssp. viridula are probably much affected by genetic drift.