Abstract
Quantifying spatial patterns of species richness is a core problem in biodiversity theory. Spiny frogs of the subfamily Painae (Anura: Dicroglossidae) are widespread, but endemic to Asia. Using spiny frog distribution and body size data, and a digital elevation model data set we explored altitudinal patterns of spiny frog richness and quantified the effect of area on the richness pattern over a large altitudinal gradient from 0–5000 m a.s.l. We also tested two hypotheses: (i) the Rapoport's altitudinal effect is valid for the Painae, and (ii) Bergmann's clines are present in spiny frogs. The species richness of Painae across four different altitudinal band widths (100 m, 200 m, 300 m and 400 m) all showed hump-shaped patterns along altitudinal gradient. The altitudinal changes in species richness of the Paini and Quasipaini tribes further confirmed this finding, while the peak of Quasipaini species richness occurred at lower elevations than the maxima of Paini. The area did not explain a significant amount of variation in total, nor Paini species richness, but it did explain variation in Quasipaini. Five distinct groups across altitudinal gradient were found. Species altitudinal ranges did not expand with an increase in the midpoints of altitudinal ranges. A significant negative correlation between body size and elevation was exhibited. Our findings demonstrate that Rapoport's altitudinal rule is not a compulsory attribute of spiny frogs and also suggest that Bergmann's rule is not generally applicable to amphibians. The study highlights a need to explore the underlying mechanisms of species richness patterns, particularly for amphibians in macroecology.
Highlights
The diversity of animal and plant species on Earth is not uniformly distributed along latitudinal and altitudinal gradients [1], and geographical gradients of diversity have long fascinated biogeographers and ecologists [2,3]
Elevational patterns of species richness Spiny frogs were distributed over a large altitudinal range with the highest altitudinal distribution of Nanorana parkeri up to 5000 m a.s.l
Species richness for the subfamily Painae, the tribes Paini and Quasipaini showed a hump-shaped pattern along altitudinal gradient: richness increased steeply, and decreased after peaking at intermediate elevations of their altitudinal ranges (Fig. 2a)
Summary
The diversity of animal and plant species on Earth is not uniformly distributed along latitudinal and altitudinal gradients [1], and geographical gradients of diversity have long fascinated biogeographers and ecologists [2,3]. The species richness-altitude relationship generally follows a decreasing or hump-shaped pattern, depending on the main attributes of scale (i.e. the unit of sampling and the geographical space covered) [5]. Growing evidence suggests that the uniformly decreasing pattern is less common than the hump-shaped pattern [5,6,7,8]. Understanding altitudinal pattern in species richness offers a fascinating opportunity to investigate the general mechanisms responsible for the distribution of biodiversity [5,9,10]
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