Abundance–occupancy and abundance–body mass relationships of small mammals in a mountainous landscape
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Mountainous landscapes are characterized by strong spatial heterogeneity, leading to increasing geographical isolation and decreasing area with elevation. Consequently, the colonization rate decreases from the low to high elevation zone, while the extinction rate shows the opposite.
Due to such changes, we test whether (1) species occur at a declining number of sites (mountains) and have a less positive abundance–occupancy relationship (AOR) in a higher elevation zone; (2) a lower proportion of rare large-bodied species (less resistant to extinction) and a more positive abundance–body mass relationship (ABR) emerge in a higher elevation zone.
Using the data of small mammals from 20 elevational gradients in the Mountainous Region of Southwest China, we compared the AORs and ABRs among the low, middle and high elevation zones. The AOR and ABR were fitted with linear and polynomial regression models. We compared endemic ratios among the different elevation zones.
The AOR was best characterized by a linear model and positive in all elevation zones. Its slope decreased from the low to high elevation zone. The quadratic model performed the best in fitting the ABR in each zone. When fitted with linear models, both the R2 and slope of the ABR increased towards the high elevation zone. The endemic ratios were significantly higher in the middle and high elevation zones.
Both the AOR and ABR in mountainous landscapes are strongly elevation-dependent. The increasing geographical isolation and decreasing area with elevation can have a high impact on macroecological patterns and processes.
KeywordsAbundance–body mass relationship Abundance–occupancy relationship Extinction Isolation Mountainous landscape Small mammal
The authors wish to thank all the pioneers who collected the small mammal data used in this study. We thank the Sichuan Luoji Mountain Nature Reserve, Sichuan Gongga Mountain Nature Reserve, Sichuan Tangjiahe Nature Reserve, Sichuan Wolong Nature Reserve, Yunnan Baima Snow Mountain Nature Reserve and Tibet Sejila Mountain National Forest Park for allowing our group to conduct the small mammal sampling. Qian Zhang provided valuable suggestions for establishing the hypothesis tested. Our study is funded by the National Natural Science Foundation of China (No. 31372177) and National Special Fund on Basic Research of Science and Technology of China (2014FY110100 and 2014FY210200). Deyan Ge is supported by the Newton Advanced Fellowship of the Royal Society, UK (Ref. NA150142).
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