A global study of the geographic range size of epiphytes

Epiphytes have long been considered to have larger geographic range sizes than terrestrial plants, yet evidence for this claim comes from studies at restricted geographic and taxonomic scales and is contrary to that of some recent studies. We examined if epiphytes have larger or smaller range sizes than terrestrial plants and tested if epiphytism is a likely driver of differences in range size globally across angiosperms. We integrated global datasets on angiosperm taxonomy, distribution, and lifeform to calculate three range size metrics. We tested if there were significant differences in mean range size between epiphytes and terrestrial plants across angiosperms and within epiphyte-rich families using ordinary and phylogenetic regression models. On average, epiphytes have larger range sizes than closely related terrestrial species, supporting the hypothesis that epiphytism favours dispersal into larger areas. However, species in families where epiphytism is prevalent tend to have small range sizes regardless of their lifeform. A high proportion of epiphytes and their close relatives are rare or have vulnerably small range sizes, yet epiphytism per se does not cause rarity. Evolutionary histories and shared traits of epiphyte-rich lineages likely underlie the observed rarity and small ranges.