Land-use change is among the top drivers of global biodiversity loss, which impacts the arrangement and distribution of suitable habitat for species. Population-level effects include increased isolation, decreased population size, and changes to mutualistic and antagonistic interactions. However, the extent to which species are impacted is determined by life history characteristics including dispersal. In plants, mating dynamics can be changed in ways that can negatively impact population persistence if dispersal of pollen and/or seed is disrupted. Long-distance dispersal has the potential to buffer species from the negative impacts of land-use change. Biotic vectors of long-distance dispersal have been less frequently studied, though specific taxa are known to travel great distances. Here, we describe population genetic diversity and structure in a sphingophilous species that is experiencing habitat fragmentation through land-use change, Oenothera harringtonii W. L. Wagner, Stockh. & W. M. Klein (Onagraceae). We use 12 nuclear and four plastid microsatellite markers and show that pollen dispersal by hawkmoths drives high gene flow and low population differentiation despite a range-wide gradient of land-use change and habitat fragmentation. By separating the contributions of pollen and seed dispersal to gene flow, we show that most of the genetic parameters are driven by hawkmoth-facilitated long-distance pollen dispersal, but populations with small, effective population sizes experience higher levels of relatedness and inbreeding. We discuss considerations for conservation efforts for this and other species that are pollinated by long-distance dispersers.