A major goal of invasion biology is to understand under what conditions exotic species thrive in the introduced range. High competitive abilities are thought to be an important characteristic of exotic species. Most invasion studies focus on the competitive ability of exotic species in the introduced range and attribute their ecological success to competitive release, but fewer studies have compared the relative competitive differences within the native range. These comparative studies are important in order to determine if competitive abilities of exotic species are strong predictors of invasion success. The little fire ant Wasmmnia auropunctata is a highly invasive species that has spread from its original range (Central and South America) to becoming a globally distributed exotic species in recent decades. It is generally accepted that island ecosystems offer weak biotic resistance to exotic species as compared to their native range. Here, we examined this empirically by comparing the relative competitive difference of W. auropunctata and locally dominant ants, between its native range of Mexico and introduced range of Puerto Rico. Resource competition was assessed between W. auropunctata and native ants under field conditions and in the laboratory. Furthermore, we compared resource competition at different temporal intervals ranging from short-term (< 2 hours) to long-term (14-days) dynamics. Our results are in contrast to common invasion predictions on island communities because we show that native species were resistant to W. auropunctata in its introduced range of Puerto Rico. We observed that the ground-foraging ant Solenopsis invicta competitive displaced W. auropunctata in Puerto Rico during short-term experiments. Meanwhile, the native arboreal ant Linepithema iniquum withstood competitive pressure from W. auropunctata. In the native range of Mexico, W. auropunctata was superior against Solenopsis Picea and Pheidole protensa species, but was outcompeted by dominant ants Solenopsis geminata and Pheidole synanthropica. This study challenges the relative importance of competitive ability in predicting invasion success. This is one of the few detailed comparative studies that examines exotic species performance between native and introduced habitats.
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