Abstract
Range-size distributions are important for understanding species richness patterns and led to the development of the controversial Rapoport’s 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 Rapoport’s rule, and a subsequent test on climatic and ambient energy hypotheses, (2) non-directional rescue effect, and a subsequent test on effect of environmental factors associated with the distribution of narrowest to widest-range species. Altitudinal species range-size distribution increased with increasing altitude and showed a negative relationship with climatic variables. These results support the altitudinal Rapoport’s 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 species with intermediate range-size, rather than narrowest or widest range-size were the main cause of a mid-peak of species richness and the non-directional rescue effect. Additionally, the richness of species with intermediate range-size was highly related to minimum temperature, habitat heterogeneity, or primary productivity. Although altitudinal range-size distribution results were similar to the phenomenon of altitudinal Rapoport’s rule, the mid-peak pattern of species richness could not be explained by the underlying mechanism of Rapoport’s-rescue effect; however, the non-directional rescue effect could explain a mid-peak pattern of species richness along altitudinal gradient.
Highlights
Understanding the pattern of species richness is related to the understanding of species range-size distribution [1,2]
To understand the underlying mechanism of Rapoport’s rule, we identified the influence of minimum temperature, vertical coverage of vegetation, and horizontal habitat diversity
Our results showed that minimum temperature was the most important factor among the variables and that altitudinal range-size distribution increased in regions with severe physiological thermal tolerance (Tables 1 and 2), supporting the climatic hypothesis
Summary
Understanding the pattern of species richness is related to the understanding of species range-size distribution [1,2]. Rapoport’s rule states that higher latitudinal species have wider latitudinal ranges than that of lower latitudinal species [3]. This phenomenon has been extended to an altitudinal gradient [4,5]. Organisms living at high latitudes or altitudinal areas, where climatic conditions are highly variable, have broader physiological thermal tolerances [10] This hypothesis proposes that organisms living in these areas will have a wider distribution range. Other ecological determinants of range-size distribution are associated with habitat heterogeneity [11,12], which can be described by the ambient energy hypothesis. The altitudinal approach for this hypothesis has not yet been applied in advanced studies
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