Global gradients of plant diversity and their ecological and historical determinants

The explanation of global diversity gradients is a central issue of ecological research. To date, the global-scale analysis of macroecological determinants of plant diversity has been primarily hampered by the availability of suitable data sets. Here, we present results from an investigation of c. 1000 mainland and c. 500 island floras worldwide. Using traditional and spatial statistical mode, we test the predictive potential of various proposed hypotheses and analyze a large number of putative abiotic determinants. We develop a combined model of global plant diversity that explains 70% of the global variation. A model of island diversity which reconciles aspects of the classical MacArthur & Wilson Theory with ecology-based approaches explains a remarkable 85% of global island diversity. We argue that in contrast to many previous arguments, there is no single factor that explains broad-scale diversity gradients. In contrast, various environmental core predictors are likely to act synergistically with water-energy dynamics playing a dominant role. Furthermore, we detect significant regional-historical effects highlighting the potential role of historical contingency on global plant diversity. A comparative analysis of flowering plants and ferns emphasizes an additional role of idiosyncratic ecological and evolutionary constraints.