We have analysed the geographical records of a representative selection of extant diatom
species from a freshwater pond. The more often a species is recorded in the ecological
literature, the greater is its apparent global distribution. One explanation is that the frequently
recorded species are globally abundant, whereas species that are infrequently recorded are
globally rare. We suggest a model in which random dispersal is the dominant force driving
large-scale distribution of species, with the rate and scale of dispersal largely determined by …