Among population variation in specialist and generalist seed predation -: the importance of host plant distribution, alternative hosts and environmental variation

Pre-dispersal seed predators can have important effects on population dynamics and trait selection in their host plants. However, the factors determining spatial variation in predation intensity are poorly known. We assessed the relative importance of host plant distribution, alternative hosts and environmental factors for among-population variation in predation in a system with three host plants, a specialist and a generalist pre-dispersal seed predator. Effects of host plant population size were relatively more important in the specialist than in the generalist seed predator. The specialist seed predator Apion opeticum, utilizing only Lathyrus vernus occurred in less than half of the patches, and specialist seed predation was influenced only by host plant population size. The generalist Bruchus atomarius was present in nearly all patches, and generalist predation was influenced by environmental factors and availability of alternative hosts. Predation on alternative hosts was not affected by L. vernus presence. The results suggest that a wide range of factors influences the strength of plant-seed-predator interactions, and that the relative importance of different factors depend on the degree of specialization. This will result in highly complex selection mosaics and coevolutionary trajectories.