Effect of area and geometric constraints on altitudinal patterns of angiosperm plant richness in Mt. Taibai, the Qinling Mountains, China

摘要

The altitudinal distribution patterns of angiosperms in Mt. Taibai, Qinling Mountains, China, were examined based on data of regional flora and Digital Elevation Model. Possible factors determining the distribution, such as geographical area effect and mid-domain effect (MDE) were assessed. The richness and density at species, genus, and family levels showed a hump-shaped pattern along the altitudinal gradient with peak at low-elevations. Similar patterns were identified for four life-forms (trees, lianas, shrubs and herbs), three biogeographical species groups (cosmopolitan, tropic and temperate), and two different range sizes (small- and large-ranged species). The endemic richness displayed a bimodal pattern with increasing altitude, but the proportion of endemism increased rapidly from low to high altitudes. The area of each altitudinal band was highly associated with the species richness, whereas the MDE could explain 87.0 and 50.3% of the richness variance for overall and endemic species, respectively. The collinearity between MDE and area could explain a large proportion (83.3%) of variance in species richness, implying the substitution between the two factors. Moreover, the explanatory power of MDE was stronger for large-ranged species than for small-ranged species. Our results confirmed that both MDE and area were all crucial factors to explain altitudinal richness patterns in Taibai Mountain, China.