Unusually large invasive seeds are spared by rodents in a Patagonian forest

Abstract

Abstract Seed predation by rodents can act as a barrier, limiting the establishment of exotic species. Predation rates of exotic seeds may depend on their attractiveness, determined by their traits and how different they are from natives. Additionally, at the naturalization stage of the invasion process, exotic seeds may escape post-dispersal predation because they are uncommon in the community. To test these ideas, we assessed granivory in a Patagonian forest, where two species with contrasting seed sizes are naturalized. Rubus idaeus seeds are of similar size to native species, whereas Prunus cerasus seeds are four times larger. The relative abundance of their seeds within the landscape is low compared to native seeds. Throughout the fruiting season, we offered seeds from all species present in the community (native and exotics), whenever they were available in the landscape. To consider the effects of vegetation structure on rodent foraging behavior, we offered seeds in areas with or without understory cover. Seed size affected the probability of removal, with rodents preferentially foraging on those of intermediate sizes. Consequently, they strongly avoided large Prunus seeds, but removed Rubus seeds at similar rates to natives. Contrary to our expectations, seed abundance did not affect predation, and hence, rarity did not confer an advantage to exotic seeds. The presence of shrub cover increased 2.3 times the removal rates compared to open areas. Concluding, the dissimilarity in seed size compared to native species and the presence of shrub cover influenced the predation pressure on exotic species within our community.