Environmental variables
To characterize the climate conditions at the sampling sites and
identify putative drivers of environment-associated selection, we
downloaded monthly data on 19 bioclimatic variables and average solar
radiation from WorldClim2 (Fick & Hijmans, 2017). A global aridity
index (Aridity) was added to our analysis of evapotranspiration
processes and rainfall deficits underlying vegetative growth (Trabucco
& Zomer, 2018). We excluded highly correlated variables with variance
inflation factors (VIF) > 10 and Pearson correlation
coefficients (r ) > |0.7|, leaving
eight climate factors for inclusion in the subsequent analyses: BIO2,
BIO4, BIO5, BIO6, BIO17, BIO18, Solar9, and Aridity.