A major goal of invasion biology is to understand under what conditions exotic species thrive in the introduced range. However, little is known about the performance of exotic species in their native ranges. Understanding how exotic species perform in their native ranges can help us better predict why some become successful invaders. In this study, we compared competitive interactions between locally dominant native ant species and the exotic little fire ant Wasmannia auropunctata in its native range of Mexico and introduced range of Puerto Rico. We conducted competition experiments between W. auropunctata and native ants in the field and in the laboratory to determine relative differences in number of workers found at baits, discovery time, and recruitment time to resources. Our results show that W. auropunctata’s ecological dominance varies between its native and introduced range. While some locally dominant ant species resisted W. auropunctata in its native range of Mexico, we found that W. auropunctata faced resistance by local ant species in the introduced range of Puerto Rico. In Mexico, the ground foraging ant Solenopsis geminata was competitively superior to W. auropunctata, while native ant species such as Pheidole synantropica, Solenopsis picea, and Pheidole protensa were all displaced by W. auropunctata during short-term experiments. Similarly, long-term experiments in Mexico showed that W. auropunctata was superior to S. picea. In Puerto Rico, the ground-foraging ant Solenopsis invicta displaced W. auropunctata in the field, while the dominant arboreal ant Linipethema iniquum was able to constrain W. auropunctata. This study revealed that the little fire ant W. auropunctata was ecologically dominant over terrestrial and arboreal ants in its native range; however, in its introduced range other species were either numerically dominant or competitively superior.