Isolated effect of each of the four predictors for the development of reproductive isolation in the Ensatina ring species: a) mitochondrial DNA, b) nuclear DNA, c) climate, and d) vegetation. Data points are pairwise comparisons between populations that contact around the ring (ten light grey points), at the mid-ring (one dark grey point) and at the terminus (two black points). Solid black lines represent the best-fit line for each predictor variable, dashed red lines designate contours of the predicted formula, and respective probabilities are denoted in the corner of each plot.
Pereira et al. BMC Evolutionary Biology 2011 11:194 doi:10.1186/1471-2148-11-194