Predicting which species are likely to become invaders in a given environment has been a central challenge in ecology and conservation biology. Invasive species can have large ecological and economic costs, thus understanding what makes an exotic species a successful invader has global significance for managing ecosystems as well as important theoretical implications for understanding community assembly. Many current approaches seek to predict successful invaders by examining the traits of introduced taxa or habitat characteristics. However, recent studies have suggested that phylogenetic relationships between potential invaders and the native community may offer better predictions of likely invaders in a given community. This approach has proven successful in multiple studies, but has thus far predominantly been tested on plants. In order to determine if this method is more broadly applicable, we tested it on two highly invaded vertebrate communities, the avifaunas of Florida and Hawaii. We used estimated branch lengths from phylogenetic trees we constructed to calculate nearest neighbor distances and mean phylogenetic distances between introduced species and the native community. We then compared these measurements to published information on the success of each introduced species using linear and logistic regression.
We predicted that successful invaders would be more distantly related to the native community based on Darwin’s naturalization hypothesis, stating that novel phenotypes would likely face less direct competition. The phylogenetic distance between an introduced species and its nearest native neighbor was not predictive of invader success in Florida. However, there was a slight, non-significant trend for greater phylogenetic distance between successful invaders and the invaded community. The relationship between the success of introduced species in Hawaii and their nearest native neighbor was highly significant, as was the relationship between success and mean phylogenetic distance. Contrary to our predictions, successful introduced species were more closely related to native species than expected by chance in the Hawaiian avifauna. This trend was observed for both the entire archipelago and for each island individually While correlative, these results suggest that pre-adaptation to local conditions (either biotic or abiotic) might be more important than competition in the establishment of invasive species on island ecosystems.