Genetic variation in the moss Homalothecium lutescens in relation to habitat age and structure

Relationships between genetic (allozyme) variation and landscape age and structure were investigated in 17 calcareous grassland demes of the moss Homalothecium lutescens (Hedw.) H. Rob. on the Baltic island of Oland. Mean within-deme gene diversity (H-S = 0.152) was moderate compared with other bryophyte studies, and the between-deme proportion of the total diversity (G(ST) = 0.100, Jost's D = 0.011) was low but significantly different from zero. Clonal mixing, measured as the proportion of two adjacent shoots having different haplotypes, was relatively high (mean 0.32 over all demes). HS was higher in old grassland fragments, but negatively related to vascular plant species richness. Allelic richness (A) was positively associated with the area of old (>= 280 years) grassland in the surroundings: although demes in old grasslands are genetically more variable than those in younger grasslands, proximity to large areas of old grassland may promote genetic variability even in younger grassland demes. The importance of management continuity for species diversity has been stressed in many earlier grassland studies. Here, we conclude that grassland fragments with a long history of grazing continuity are also positively associated with variability at within-species level, as exemplified by the bryophyte H. lutescens