Population structure varies among 4 western North American bumble bee species.

This article focuses on the population genetic structure and habitat connectivity of four bumble bee species—*Bombus flavifrons*, *B. melanopygus*, *B. mixtus*, and *B. sylvicola*—across the Rocky and Cascade Mountains of western North America. Using microsatellite markers and habitat suitability models (HSMs), the study found significant genetic differentiation among populations of all species, with western populations generally more genetically distinct from inland ones. Isolation by resistance (IBR), which incorporates habitat suitability, better explained genetic structure than isolation by distance (IBD) for *B. flavifrons* and *B. mixtus*, highlighting the importance of habitat connectivity in maintaining gene flow. The findings also underscore species-specific responses to landscape and climatic factors, with implications for conservation strategies addressing genetic isolation driven by climate change and habitat fragmentation.