What determines niche widths in communities structured by habitat heterogeneity? Previous work suggests that the relative success of habitat generalists and specialists depends on the distribution and abundance of habitat types, as well as the phenotypic trade-offs experienced by species exploiting different habitats. However, other factors may also play a role. Here I model the effect of resource conversion efficiencies of individual foragers on community structure, including niche widths of residents and successful invaders. I construct a resource-consumer model of flexible (optimal) foragers exploiting a continuum of habitat types, in which consumer densities, behaviors and conversion efficiencies influence resource levels. The model predicts that an increase in resource conversion efficiency by all community members increases community invasibility, and promotes the competitive exclusion of habitat generalists by habitat specialists. An adaptive dynamics analysis of the model predicts that increased resource conversion efficiency promotes evolutionary bifurcation, followed by increased habitat specialization and species invasion.