Distance between populations
Greater distance between populations should correspond to greater genetic differentiation based on an isolation by distance model (Wright, 1943). Thus, we also included in our null model the maximum distance between populations used in each study. We calculated this based on the coordinates of the two most distant populations. When this was not available, we used the scale bar of maps showing sampled populations. Distance varied from 0.01–9900 km (mean=703 ± 1077 SD).