Positive interactions between invasive species may facilitate and amplify the invasive success of each interacting partner, leading to “invasional meltdowns.” Coastal tallgrass prairies, imperiled ecosystems along the Gulf Coast, are currently under threat by non-native species species from multiple trophic levels: the Chinese tallow tree (Triadica sebifera L.), the omnivorous tawny crazy ant (Nylanderia fulva Mayr), and most recently, an adventive, hypermetamorphic, herbivorous moth (Caloptilia triadicae Hodges). Previous research demonstrated that invasive Chinese tallow induces extrafloral nectar (EFN) in response to specific, chewing herbivores, and tawny crazy ants have been observed consuming tallow EFN on the prairie. However, the nature of interactions between these three species is currently unknown, and studies of tri-trophic interactions between spatially-associated, non-coevolved invasive species are underrepresented in the ecological literature. We hypothesized that invasive Chinese tallow, when attacked by the non-native moth, confers a nutritive resource to the ecologically dominant invasive ant. To determine the nature of the interactions between these species, we experimentally manipulated EFN induction in potted Chinese tallow saplings using three levels of Caloptilia infestation and conducted complementary laboratory feeding trials with tawny crazy ant workers.
Results/Conclusions
Our lab and field experiments suggest that these three introduced species are indeed having positive interactions with one another in this threatened ecosystem. Because these species co-occur across a large area in the southeastern United States, our results could have large implications for management of these invasions in multiple ecosystems. Management of a single invader may be insufficient if these interactions facilitate the invasional success of all three at large spatial scales.