Island biogeography theory and the habitat heterogeneity jointly explain global patterns of Rhododendron diversity

Mountain biodiversity is of great importance to biogeography and ecology. However, it is unclear what ecological and evolutionary processes best explain the generation and maintenance of its high levels of species diversity. In this study, we determined which of six common hypotheses (e.g., climate hypotheses, habitat heterogeneity hypothesis and island biogeography theory) best explain global patterns of species diversity in Rhododendron. We found that Rhododendron diversity patterns were most strongly explained by proxies of island biogeography theory (i.e., mountain area) and habitat heterogeneity (i.e., elevation range). When we examined other relationships important to island biogeography theory, we found that the planimetric area and the volume of mountains were positively correlated with the Rhododendron diversity, whereas the ‘mountains-to-mainland’ distance was negatively correlated with Rhododendron diversity and shared species. Our findings demonstrate that Rhododendron diversity can be explained by island biogeography theory and habitat heterogeneity, and mountains can be regarded as islands which supported island biogeography theory.