Connectivity in a Karst landscape: genetic diversity and population differentiation in the rare plant Bird's Foot sedge, <i>Carex ornithopoda</i> Willd.

Within Britain the Karst landscape is predominantly upland and is characterised by high nature value grasslands which are home to many plant species of conservation interest. One such species is Carex ornithopoda (Bird's Foot sedge) which is found in a limited number of populations in these upland Karst regions. Several of these populations are clustered together with a handful of distant populations. The species is at the western edge of its range in Britain. By comparison Estonia is close to the centre of the range. Sampling of six to twenty individuals of C. ornithopoda from eight British populations and five Estonian populations was undertaken. Individuals were genotyped using nuclear microsatellites over six loci. British and Estonian populations had similar levels of mean genetic variation and also had similar deficits of observed heterozygotes. However British populations had higher levels of unique multi locus genotypes within populations alongside reduced genetic evenness. Isolation by distance is occurring in Britain to some degree, although long distance dispersal is also noted. There is some differentiation of proximal populations in Britain which is absent in Estonia. It is suggested that the similarity and evenness of Estonian populations is due to high levels of gene flow facilitated by intermediate populations. Local gene flow may occur over short distances by pollen or ant transport of seeds. Genetic drift has partly led to some genetic dissimilarity between populations in Britain. Extensive sheep grazing may also limit pollen or seed production and hence restrict gene flow. Dispersal via water is likely to be responsible for long distance dispersal, though other, animal mediated, long dispersal mechanisms is also possible.