Range size, dispersal and niche breadth in the herbaceous flora of central England

It has been suggested that rare species differ from related common species in a variety of traits, including (among others) niche breadth and dispersal ability. We set out to test these ideas in the flora of central England. We used two measures of range: number of hectads in Britain (national range) and number of 1 km2 in a 3000-km2 area of central England (local range). In each case we regressed phylogenetically independent contrasts in geographical range against contrasts in range of germination temperature (one aspect of fundamental niche breadth), terminal velocity of dispersule (a measure of wind dispersal capacity), seed weight and specialism index (a measure of the diversity of habitats exploited in central England). Seed weights and germination temperature were known for 263 species, specialism index for 261 and terminal velocity for 178. Specialism index explained by far the largest part of the variance in local and national range. Seed weight, terminal velocity and germination temperature each explained only 2-4% of the variation in local range, and none of the variation in national range. Most previous attempts to relate niche breadth and dispersal ability to range have concerned animals. There is little convincing published evidence for plants, and in the British herbaceous seed plants studied here the best predictor of range was diversity of habitats exploited. This pattern was independent of phylogeny.