To avoid
model overfit, we reduced the number and correlation of environmental
variables used for model calibration via a principal component analysis
(Peterson et al., 2011), inwhich we retained the first 6 components
for ENM calibration. These data layers summarized 99.99% of total variance
in the original environmental variables (Supplementary material
S1). We calibrated the niche model based on the present-day distribution
of U. thibetanus. We represented the species' distribution using
3000 random points distributed across the species' present-day distributional
area, covering 1.34 × 106 km2, as proposed by the International
Union for Conservation of Nature