Evaluation of current gene flow and resistance surfaces
Contemporary gene flow was estimated using BayesAss (Wilson & Rannala, 2003), which estimates directional migration rates over past generations using multilocus genotypes and a Bayesian approach. Mixing parameters were altered to tune acceptance rates within an adequate range. Aside from estimating gene flow between populations, we adopted an estimated effective migration surfaces (EEMS) algorithm (Petkova, Novembre, & Stephens, 2016) to visualize geographic regions deviating from isolation by distance (IBD), i.e., to identify areas where genetic similarity decays faster than expected for a given geographic distance (barriers) and areas where genetic similarity decays more slowly than expected for a given geographic distance (corridors). Parameters for executing BayesAss and EEMS are presented in the SMM.