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

Abstract

Seed predation by rodents can act as arecruitment barrier during community assembly, lim-iting the establishment of exotic species. Predationrates of exotic seeds may depend on their attractive-ness, determined by their traits, and how differentthey are from natives. Additionally, at the naturaliza-tion stage of the invasion process, exotic seeds mayescape post-dispersal predation because they are rarein the community. To test these ideas, we assessedgranivory in a Patagonian forest, where two specieswith contrasting seed sizes are naturalized. Rubusidaeus seeds are of similar size of natives, whereasPrunus cerasus seeds are four times larger. The relative abundance of their seeds within the land-scape is low compared to native seeds. Throughoutthe fruiting season, we offered seeds from all speciespresent in the community (native and exotics), when-ever they were available in the landscape. To considerthe effects of vegetation structure on rodent foragingbehavior, we offered seeds in areas with and withoutunderstory cover. We found a hump-shaped relation-ship between predation rates and seed size. Conse-quently, rodents strongly avoided large exotic Pru-nus seeds, but removed Rubus seeds at similar ratesto natives. Contrary to our expectations, seed abun-dance did not affect predation, and hence, rarity didnot confer an advantage to exotic seeds. The presenceof shrub cover increased 2.3 times the removal ratescompared to open areas. We suggest that the dissimi-larity in seed size compared to native species and thepresence of shrub cover influenced predation pressureon exotic species within our community.