Invasive Ants Generate Heterogeneity in Patterns of Seed Survival

Although studies often focus on the direct effects of invasive species on native taxa, invasive species may also alter interactions among native species. For example Solenopsis invicta, the red imported fire ant, may directly alter native seed survival by consuming seeds, but also indirectly alter seed survival, by altering the abundance and/or behavior of native granivores. We tested the effects of invasive S. invicta on rodent and arthropod granivory by quantifying seed removal from seed depots that differed in granivore access (arthropods and rodents or arthropods only) and distance from an S. invicta mound (0.1 m or 4.0 m). We hypothesized the effect of S. invicta on native granivores would be stronger at depots located near (0.1 m) a mound than at depots located 4.0 m from a mound. Use of two different seed species (Rubus cuneifolius and Prunus serotina) allowed us to evaluate the consequences of S. invicta for small-seeded plant species consumed by both arthropods and rodents (R. cuneifolius) as well as for large-seeded species that can only be consumed by rodents (P. serotina). We found overall removal of P. serotina was low, regardless of seed depot location or exclosure type. Near S. invicta mounds, the removal of R. cuneifolius was also low, with no difference between depots that allowed or excluded rodents. In contrast, removal of R. cuneifolius by arthropods 4.0 m from a mound was nearly twice that of removal next to a mound but only when rodents were excluded. Our results indicate S. invicta may create hotspots of granivory by native arthropods in the areas between S. invicta mounds, but these effects may not extend to large-seeded plants that are consumed by rodents. By influencing seed survival as a function of plant species and proximity to a mound, nonnative S. invicta generates heterogeneity in native seed survival, which may affect plant community composition.