Families with highest proportions of rare species are not consistent between floras

Aim: In this study we compare the incidence of rarity within lineages between three floras: Australia, North America and New Zealand. Methods: We used published data for absolute numbers of species and for numbers of rare species to ask three questions: 1. Do families have similar proportions of rare species in different floras? 2. Can proportions of rare species within families be interpreted with reference to biogeographic history of particular floras? and 3. Is the proportion of rare species consistent between families and genera within each flora? Results: Within families in each flora, genera usually had similar proportions of rare species; indicating processes determining rarity are in general not operating differentially within families. However, in comparisons within-family between floras, approximately 62% of comparisons showed significant differences in the proportion of rare species. Main conclusions: These results imply that there are no general rules whereby the particular traits a family possesses are conducive to rarity wherever they occur. Rather, such attributes must exert influence conditionally, in conjunction with the biogeographical and competitive setting where speciation and extinction or persistence has occurred.