Abstract
We compare four different models describing the dependence of species richness on area, maximum altitude in the island and its latitude, using the data on orchid species richness from a global review of islands. Besides the commonly used factors (area, latitude), we also use maximum altitude, because it was the most important factor for orchids in Ackerman et al. (2007).
Area and altitude of the highest peak are significantly positively correlated with the number of orchid species present on an island. Significance of latitude not surprisingly disappears when the latitudinal extent of an archipelago is small.
We show that the best multivariate model for prediction of orchid species richness is the classical species-area relationship combined with linear dependence of the log number of species on altitude of the highest peak and latitude.