Between clades niche divergence
We used the first three dimensions of a PCA of current climatic
conditions (84.97% of variance; see Supporting Information for details)
to calculate niche overlap between populations. Between-clade climatic
niche divergence was detected as overlap values were significantly lower
than expected by chance for all clade pairs within species (Figure 2a).
Overlap values ranged from 0.000 to 0.302 (Supporting Information). In
general, northern clades were located towards positive values of PC1 and
PC2 (i.e. inhabit cooler environments with higher winter precipitation),
whereas southern clades were mostly on negative values of PC1 and PC2
(i.e. warmer environments with higher summer precipitation). Significant
differences were detected for the niche breadth between southern,
northern and unstructured clades (Supporting Information). In general,
northern and unstructured clades presented wider niches than southern
clades (Figure 2b).