Environmental analysis
To evaluate environmental variation between El Pardo and Navacerrada, we
computed the score of each cell that an individual would have to cross
in a theoretical straight-line migration event following valley bottoms
on a principal component analysis (PCA) that combined all Bioclim
environmental variables (2.0 dataset; cell resolution = 1x1 km; Booth et
al. 2014) using R core (R Core Team, 2013). This PCA has been previously
used to summarize environmental variation (temperature and humidity)
across all the species’ range, yielding a single principal axis that
opposed dry and warm cells to wet and cold ones (Llanos-Garrido et al.,
2021). To assess the environmental gradient between these populations,
we also considered the scores at the cells occupied by the populations
themselves.