Nora M Cavanaugh, Amy E Zanne, William K Cornwell

Epiphytes are a large and understudied part of global diversity. Classic work by Gentry and Dodson argued that Neotropical, mid-elevation forests are centers of diversity for this growth form. We assessed this hypothesis with modern global geospatial and climatic datasets. By connecting growth form and occurrence data with climatic records at the same locations, we quantified spatial and climatic distributions of epiphyte species richness. Latitude was a powerful driver of epiphyte distributions, with peaks at the equator; here, epiphytes contributed significantly to vascular plant species richness with greatest prevalence at mid elevations and in the Neotropics. Climatically, precipitation was a stronger determinant than temperature as to where epiphytic species thrive. The study provides robust support for the hypotheses that plant diversity in Neotropical, mid-elevation forests is unusually concentrated in the epiphytic growth form, and the lower proportion of epiphytic diversity elsewhere may have both physiological or biogeographic explanations. The particular features of climate change in Neotropical mid-elevation habitats, and the implications for epiphyte diversity, are worthy of urgent research.