Abstract:

The Rapoport’s rule predicts that altitudinal range size of species increases with altitude. Using a dataset on range size of vascular plant species across an altitudinal gradient at Mt. Shennongjia, central China, we analyzed altitudinal patterns of all species richness, and four quarters of species classified by an order of increasing range size. Previous four methods and the midpoint method modified by this study were applied to explore the relationship between range size and range midpoint along an altitudinal gradient to test the Rapoport’s rule. Altitudinal variation in vascular plant species richness on Mt. Shennongjia was hump-shaped with a peak at 1,100-1,200 m a.s.l. A similar pattern was found for the four quarters of species, and peak value of the species richness shifted to lower elevations with decreased range size of quarters. Stevens’ method, Pagel’s method, and cross-species method all supported the Rapoport effect, while the midpoint method generated a quadratic pattern, suggesting a mid-domain effect. The sectionalized midpoint method presented inconsistent results, even after removing the mid-domain effect. Our results imply that tests of Rapoport’s rule are limited by methodological considerations, and that comparisons among more empirical tests are needed in order to generate conclusive insight into altitudinal patterns of species range size, and the mechanism shaping such patterns.

Key words: altitudinal gradients, species richness, range size, Rapoport’s rule, mid-domain effect