Sample locations and modeled ranges. (A) Eight big-leaf mahogany populations (22), and modeled range following the Central American landmass from the Isthmus of Tehuantepec south through Panama (shading); extension of modeled range further north or south did not alter results. Sample sizes ranged from 16 to 55 individuals per population. (B) Twelve wolverine populations (23), and contiguous wolverine range in the western United States and Canada. Sample sizes ranged from 14 to 67 individuals per population. All results were consistent using alternative map projections, raster cell sizes, and genetic distance measures.

Circuit theory outperforms standard models of genetic differentiation among mahogany populations. Range maps illustrate how pairwise isolation is measured under the competing models between two example populations (Nuevo Becal and Tonosí), and scatterplots show performance of the models for all population pairs. Models compared are one-dimensional IBD (A), which assumes habitat to be arranged in an infinite linear array; two-dimensional IBD (B), which assumes habitat to be arranged in an infinite plane; LCP (C), which incorporates spatial heterogeneity but assumes differentiation to vary with distance measured along a single, optimal path; and IBR (D), which predicts greater gene flow and less genetic differentiation with multiple pathways and wider habitat swaths connecting populations. (D Inset) Habitat modeled as a conductive surface. Open circles indicate pairwise comparisons including Tonosí; filled circles indicate comparisons among the remaining seven populations. Linear regression lines include all populations.

Circuit theory outperforms standard models of genetic differentiation among wolverine populations. Range maps illustrate how pairwise isolation is measured under the competing models between two example wolverine populations (Idaho and Manitoba). Models compared are two-dimensional IBD (A), the better justified IBD model (see IBD Predictions under Methods), LCP (B), and IBR (C). Open circles indicate pairwise comparisons including Idaho. Linear regression lines include all populations.