Attributes of rarity in a regional bryophyte assemblage

In order to help understand rarity in bryophytes, the present study investigates attributes of 430 taxa (ranging from very rare to very common) within a region of north-west England (UK). Results show that rarity is largely congruent between the scale of the study area and the British Isles, even though the area of the former is only 0.7% of the latter. Two indicators of niche breadth are negatively correlated with rarity at different spatial scales and for different groups of taxa, suggesting that rare species are able to exploit a relatively narrow range of habitats and substrates (and hence occur in fewer places). Significant positive correlations exist between sporophyte production and range-size for mosses at the scale of the study area and for liverworts at the scale of the British Isles, which may be linked with dispersal ability. Also, monoicous mosses at the scale of the British Isles are rarer than dioicous species, possibly due to processes associated with self-fertilization.