Abundance–occupancy and abundance–body mass relationships of small mammals in a mountainous landscape

Abstract

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.