Spatial variation in ant and rodent post-dispersal predation of vertebrate-dispersed seeds

1. Post-dispersal predation of vertebrate-dispersed seeds has received little attention in the Mediterranean region. We investigated the spatial variation in post-dispersal seed predation of vertebrate-dispersed plants and its potential implications for plant diversity in fleshy fruited plant communities of southern Spain. 2. An experiment was conducted in forests and open scrubland at mid- and high elevations to explore: (a) the possibility of differential seed predation by rodents and granivorous ants; (b) the spatial variation, between and within habitats, in post-dispersal seed predation and predator abundance; and (c) whether the spatial distribution of predation covaries among plant species. 3. Rodents and granivorous ants proved to be important predators of vertebrate-dispersed seeds, and showed significant variation in their preferences for different seed species. Granivorous ant preferences depended on seed size, as seeds heavier than 20 mg were hardly ever removed. Rodents were indifferent to seed size. 4. Sites safe from predators were more frequent at mid-elevations. In contrast to other temperate communities, successional status (open scrubland vs forest) did not determine the probability of predation, probably because ants are more important as seed predators in the early successional stages of Mediterranean habitats than in other temperate communities. The large-scale variations in the occurrence of safe sites for the seeds depended on resource abundance rather than on predator abundance. 5. We found a significant interaction in seed predation rates between microhabitat and seed species at mid-elevations, but not in high-elevation habitats, implying stronger covariance across plant species in the microhabitats adequate for recruitment (e.g. with lower predation risk) at high elevation. This pattern may contribute to the differential plant diversity at mid- and high elevations in Mediterranean fleshy fruited plant communities. Theoretical models predict that seed predators may contribute to the maintenance of species diversity if the spatial distribution of safe sites from predators is uncorrelated across plant species, as it was at mid-elevations.