The diets of predators should reflect interactions between their behavioural and anatomical constraints and the availability and accessibility of prey, although feeding preferences may also reflect adaptation to locally abundant prey, particularly in closed populations. On the south-east coast of Australia, the whelk Haustrum vinosum (Lamarck, 1822) and its prey communities provide a model system in which to test the effect of variation in prey availability on diet and dietary preferences. Haustrum vinosum is a direct developing species, forming effectively closed populations, with the potential for local adaptation at local and regional scales. Here we show that populations of whelks east and west of a biogeographical barrier encounter different prey assemblages, and have different feeding patterns and apparent prey preferences. We then use a prey choice experiment to test for evidence that H.vinosum from three populations west of the barrier display an inherent preference for its most frequently encountered western prey species, the mussel Brachidontes rostratus (Dunker, 1857), over a novel prey, the barnacle Tesseropora rosea (Krauss, 1848). We detected no prey preference within any population, suggesting past association with B.rostratus did not influence prey selection. Our data support the hypothesis that predators with limited dispersal and high population differentiation are able to maintain flexible generalist foraging patterns, even when they encounter novel prey.