Considerations on model inference
Phylogenetic multiple regressions allowed us to evaluate the unique effect of each predictor on FST while correcting for phylogenetic autocorrelation, which had not been accomplished in previous broad-scale studies. Additionally, we note that after adding the factor latitudinal region, the scaling parameter that corrects for phylogenetic autocorrelation (λ fit in Table 1) became insignificant. This suggests that latitudinal region decreases the phylogenetic autocorrelation in the residuals modeled by our phylogenetic regressions (Freckleton, 2009). In fact, an alternative across-species multiple regression of model 7 (i.e., a linear model assuming phylogenetic independence) yielded identical results with indistinguishable fit to the data (ΔAIC=1.9). We suspect that region captured important phylogenetic information in FST and species traits; within each regional species pool, lineages share strong biogeographic and phylogenetic affinities. Put another way, we think that regional affiliation is the most important underlying factor influencing FST values at a global scale, and when not included, phylogenetic signal becomes a proxy for latitudinal region due to the tendency for closely related species to occur in similar regions.