Community composition is determined by attributes of the environment, individual species, and interactions among species. We studied the distributions of a seed weevil and its parasitoid and hyperparasitoid wasps in a fragmented landscape. The occurrence of the weevil was independent of the measured attributes of the landscape (patch connectivity and resource availability). However, between habitat-patch networks, weevil density decreased with increasing parasitism, suggesting top-down control, especially in the north. Parasitism was mostly due to a specialist and a generalist that appeared to compete strongly. This competitive interaction was strongest at high patch-connectivity, perhaps due to a trade-off of local competitive ability and dispersal. Finally, the abundance of the generalist hyperparasitoid was unrelated to landscape or host-species abundance. The snapshot presented by these data can best be explained by top-down effects, interactions among species, host ranges, and patch configuration in the landscape, but not by local host-plant abundance.