Abstract
We report on the species richness patterns of epigaeic beetles (Coleoptera: Carabidae and Staphylinidae) along a subtropical elevational gradient of Balang Mountain, southwestern China. We tested the roles of environmental factors (e.g. temperature, area and litter cover) and direct biotic interactions (e.g. foods and antagonists) that shape elevational diversity gradients. Beetles were sampled at 19 sites using pitfall traps along the studied elevational gradient ranging from 1500 m–4000 m during the 2004 growing season. A total of 74416 specimens representing 260 species were recorded. Species richness of epigaeic beetles and two families showed unimodal patterns along the elevational gradient, peaking at mid-elevations (c. 2535 m), and the ranges of most beetle species were narrow along the gradient. The potential correlates of both species richness and environmental variables were examined using linear and second order polynomial regressions. The results showed that temperature, area and litter cover had strong explanatory power of beetle species richness for nearly all richness patterns, of beetles as a whole and of Carabidae and Staphylinidae, but the density of antagonists was associated with species richness of Carabidae only. Multiple regression analyses suggested that the three environmental factors combined contributed most to richness patterns for most taxa. The results suggest that environmental factors associated with temperature, area and habitat heterogeneity could account for most variation in richness pattern of epigaeic beetles. Additionally, the mid-elevation peaks and the small range size of most species indicate that conservation efforts should give attention to the entire gradient rather than just mid-elevations.
Highlights
Variation of species richness patterns along environmental gradients has long been of interest to biologists, and understanding the mechanisms underlying that variation is one of the fundamental questions in ecology [1,2]
Species Richness Pattern along the Elevational Gradient A total of 74416 epigaeic beetles belonging to 260 species were sampled within the 58 studied plots at 19 sites along the elevational gradient (Table S1)
There were 25% (64 spp.) of beetle species found at only a single elevation, but three species (Pterostichus expedita, Pterostichus noguchi and Philonthus azuripennis) occurred at the whole elevational gradient (Table S2)
Summary
Variation of species richness patterns along environmental gradients has long been of interest to biologists, and understanding the mechanisms underlying that variation is one of the fundamental questions in ecology [1,2]. Of these patterns, species richness along the latitudinal gradient is the most striking and perhaps best documented pattern [3,4], and many hypotheses and underling mechanisms have been proposed to explain it, such as energy availability, evolutionary time, habitat heterogeneity, area and geometric constraints [3,5,6]. As the global majority of terrestrial organisms, just a few studies on insects have been examined richness patterns along elevational gradients, focusing on specific taxa such as ants [18,19], butterflies [20], moths [21,22], and dung beetles [23,24], and knowledge of elevational richness patterns and underlying causes for most insects are still very poor
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