**Estimated Effective Migration Surfaces** Here we provide input files for two independent runs of the EEMS program, along with outputs, and our resulting figures. We visualized spatial patterns of gene flow and genetic diversity using EEMS (ESTIMATED EFFECTIVE MIGRATION SURFACES; Petkova et al. 2016), a method that uses genome-wide SNP variation and locality information to highlight regions where genetic similarity decays more quickly than expected under isolation by distance. The number of migration routes and deme sizes is specified through a grid size, and resistance distance is used to approximate the expected dissimilarity between two samples. These estimates are interpolated across geographic space to provide a visualization of levels of gene flow and diversity across regions. We chose a deme size of 700 and ran two independent analyses using RUNEEMS_SNPS, with a burn-in of 1,000,000 and MCMC length of 20,000,000. We combined the two independent runs per deme size, assessed convergence, and generated surfaces of effective diversity (q) and effective migration rates (m) using the ‘R EEMS Plots’ R package (Petkova et al. 2016).