Altitudinal range-size distribution of breeding birds and environmental factors for the determination of species richness: An empirical test of altitudinal Rapoports rule and rescue effect on a local scale

Range-size distributions are important for understanding species richness patterns and led to the development of the controversial Rapoports rule and Rapoport-rescue effect. This study aimed to understand the relationship between species richness and range-size distribution in relation to environmental factors. The present study tested the following: (1) altitudinal Rapoports rule, (2) climatic and ambient energy hypotheses, (3) non-directional rescue effect, and (4) effect of environmental factors on range-size group. Altitudinal species range-size distribution increased with increasing altitude and showed a negative relationship with climatic variables and habitat heterogeneity, and a positive relationship with primary productivity. These results support the altitudinal Rapoports rule and climatic hypothesis; however, they do not fully support the ambient energy hypothesis. Results from testing the non-directional rescue effect showed that the inflow intensity of species from both directions (high and low elevations) affected species richness. And we found that the 2nd and 3rd quartile species distribution were the main cause of a mid-peak of species richness and the non-directional rescue effect. Additionally, the 2nd quartile species richness was highly related to minimum temperature and possessed thermal specialist species features, and the 3rd quartile species richness was highly related to habitat heterogeneity and primary productivity. Although altitudinal range-size distribution results were similar to the altitudinal Rapoports rule, the mid-peak pattern of species richness could not be explained by the Rapoports-rescue effect; however, the non-directional rescue effect could explain a mid-peak pattern of species richness.