Spatial patterns and determinants of Moraceae richness in China

Aim Understanding large-scale patterns of biodiversity and their drivers remains central in ecology. Many hypotheses have been proposed, including hydrothermal dynamic hypothesis, tropical niche conservatism hypothesis, Janzen’s hypothesis and a combination model containing energy, water, seasonality and habitat heterogeneity. Yet their relative contributions for groups with different lifeforms and range sizes remain controversial, which has limited our ability to understand the general mechanisms underlying species richness patterns. Here we evaluate how lifeforms and species range sizes influence the relative contributions of these three hypotheses on the species richness patterns of a tropical family Moraceae. Methods The distribution data of Moraceae species at a spatial resolution of 50 × 50 km and their lifeforms (i.e. shrubs, small trees and large trees) were compiled. Then the species richness patterns were estimated for the entire family, different life forms and species with different range sizes separately. The effects of environmental variables on species richness were analyzed, and relative contributions of different hypotheses were evaluated across life forms and species range size groups. Important Findings The species richness patterns were consistent across different species groups and the species richness was the highest in Sichuan, Guangzhou and Hainan provinces, making these provinces the hotspots of this family. Climate seasonality is the primary factor in determining richness variation of Moraceae. The best combination model gave the largest explanatory power for Moraceae species richness across each group of range size and life forms followed by the hydrothermal dynamic hypothesis, Janzen's hypothesis, and tropical niche conservatism hypothesis. All these models have a large shared effects but a low independent effects (<5%), except rare species. These finding suggest a unique patterns and mechanisms underlying rare species richness. Our study provides a theoretical basis for the protection of the Moraceae species, especially the rare ones in China.