Plant communities on granite outcrops are prone to water and nutrient limitations because of the shallow soils and high summer-temperatures characteristic of that habitat. Thus, resource availability is expected to influence plant performance on these sites. Here, we sought to determine if low resource-availability (water and nutrients) acts as a selective agent in natural populations of Helianthus porteri (Porter's Sunflower), a granite-outcrop endemic. We conducted field observations of growth and survival for 3 years in 3 populations spanning the species' range. We found that survival to flowering was correlated with soil-water availability (estimated by plant predawn water-potentials; Ψ_pd), and that drought severity (estimated by survival and Ψ_pd) differed among populations, suggesting the populations could be adaptively differentiated for resource-use traits. However, in a greenhouse common-garden experiment, the population that experienced the greatest drought severity in the field did not exhibit traits associated with greater drought resistance, and all 3 populations responded similarly to water and nutrient limitations. Thus, although drought influences survival in Porter's Sunflower, populations do not appear to be adaptively differentiated with respect to resource availability.