Patterns and underlying mechanisms of non-volant small mammal richness along two contrasting mountain slopes in southwestern China

Abstract

The species richness patterns of small mammals and the processes shaping them in two gradients of a mountain with different spatial and climatic characteristics were examined using standard sampling scheme. We trapped 2,006 small mammals representing 37 species, along elevational gradients on both western and eastern slopes of the Ailao Mountains, Southwest China. Using mid-domain effect model, model selection and model averaging, we examined the effects of slope, area, mean annual temperature (MAT), mean annual humidity (MAH), productivity, plant species richness (PSR) and the mid-domain effect (MDE) on the patterns of small mammal diversity. The hump-shaped patterns were favored along the elevational gradient, but shapes of diversity curves were different on the contrasting slopes. Area and productivity were the most important factors in explaining the variation of total species richness. However, for each specific group of small mammals (i.e. insectivores vs. rodents, large-ranged vs. small-ranged species, endemic vs. non-endemic species), the peaks of species richness and their primary drivers varied. The major explanatory factors for richness pattern of each small mammal group were not significantly different between the slopes, suggesting the existence of the general underlying mechanisms on two slopes of a mountain.

Small mammal species richness and turnover along elevational gradient in Yulong Mountain, Yunnan, Southwest China

“…When the total species are divided into different subsets, the MDE and the energy‐related models were also supported as the best model(s) for three and four of the six subsets of small mammal groups, respectively (Table ). It is not surprising that the energy hypothesis is supported in our data, as a positive relationship between diversity and productivity of small mammals was frequently reported by previous studies (Chen et al, ; McCain et al, ). MDE has generated considerable controversy because of the high variable explanatory power (McCain, ), even in studies on small mammals (Hu et al, ; Rowe, ; Wu, Yang, et al, ).…”

“…The overall species richness of small mammal exhibited a hump‐shaped pattern along the elevational gradients, with a distinct peak at 3,200 m and 3,400 m (Table ; Figure ). Such a pattern is frequently reported in the Hengduan Mountains for frogs (Fu et al, ), birds (Wu, Colwell, et al, ), as well as small mammals (Chen et al, ). These results suggest the hump‐shaped pattern might be the general richness pattern in the Hengduan Mountains.…”

Small mammal species richness is directly linked to regional productivity, but decoupled from food resources, abundance, or habitat complexity

“…This mid‐elevational species richness trend in small mammals is consistent for other small mammal studies in the mountains of the south‐western USA and across the globe, many of which also detected a positive productivity–species richness relationship (e.g. Chen, He, Cheng, Khanal, & Jiang, ; McCain, , ; Rowe, ). Despite the strong productivity–species richness relationship in mammals, this is the first test of the mechanistic underpinning of that relationship other than bivariate analyses.…”

“…Montane mammals do appear to track a high‐NPP climatic optimum (e.g., Chen et al., ; McCain, ; Rowe, ), but this optimum could be either ecologically caused by elevational filtering by dispersal over relatively short time periods (Francis & Currie, ; McCain, ), or by climatic niche conservatism within which the clades evolved (Wiens & Graham, ; Wiens et al., ). Direct physiological limits appear less likely as a mechanism underlying this productivity–species richness pattern, as it is difficult to propose physiological limits tied to productivity, rather than temperature (Evans, Greenwood, et al., ; MacArthur, ).…”

“…Discerning between the contemporary climate versus niche conservatism drivers of a direct mechanism is the next challenge. As a mammalian midelevation climatic optimum is nearly universal across mountains in the tropics and temperate zone (Chen et al., ; McCain, ; Rowe, ), presumably the species within these clades from the various mountainous regions have different regional species pools with divergent underlying evolutionary histories and climatic niche evolution. Such reasoning then suggests that mammals would be assorting more strongly to contemporary climate (e.g.…”