Quaternary and pre-Quaternary historical legacies in the global distribution of a major tropical plant lineage

Aim The relative importance of current climate and past historical legacies is hotly debated. Here, we assess their role in determining the global distribution and diversity patterns of palms (Arecaceae), a widespread, species-rich group of keystone ecological importance in tropical ecosystems. Location Global. Methods We assembled country-level species lists world-wide and compiled associated data on potential contemporary environmental drivers (current climate, habitat heterogeneity, area, and insularity), Quaternary glacialinterglacial climate change and major biogeographic regions to evaluate to what extent the global distribution and species richness patterns in palms reflect Quaternary climatic oscillations or regional effects reflecting pre-Quaternary legacies. We also assessed for the first time if historical legacies differ between continents and islands, providing novel insights into determinants of insular species richness. Results Palm species richness was significantly affected by Quaternary climate changes and further differed between biogeographic regions even when both current environmental conditions and Quaternary climate changes were accounted for. In contrast, global limits to the distribution of the palm family were best explained by current temperature while biogeographic regional differences were unimportant and Quaternary climate change caused only a small constraint. Historical legacies were weak on islands, with only a small regional effect and no effect of Quaternary climate changes. Main conclusions Strong historical legacies supplement current environment as determinants of palm species richness. These primarily comprise pre-Quaternary historical effects, reflected in low African species richness (possibly linked to pre-Quaternary extinctions) and outstandingly high Neotropical and Indomalayan palm species richness (possibly linked to these regions' long-term climatic suitability for palms). In contrast to species richness, the global distribution of the family range is largely in equilibrium with current climate. The small historical effects on islands are consistent with climatic buffering from their oceanic environment.