Integrating mutualism into the study of ecological communities is likely to be critical to understanding community dynamics and to predict the consequences of anthropogenic changes to ecosystems. Invasive species are among the greatest of these threats to global biodiversity. Throughout the Pacific, the invasive ant Anoplolepis gracilipes associates mutualistically with Morinda citrifolia, a native plant with extrafloral nectaries (EFN). I tested the hypothesis that these interactions can mediate invader impacts Anoplolepis gracilipes abundances were positively correlated with the dominance of EFN-bearing plants per site and negatively correlated with the species richness of native ants. Additionally, A. gracilipes displayed a higher magnitude of responses to nectar than other dominant ants. Mutualisms also had significant impacts on the structure of arthropod communities. These effects were strongest when A. gracilipes dominated local ant assemblages. These results suggest that novel mutualisms between invasive and native species can facilitate the impacts of invasions on communities.