Differential interspecific territoriality and the invasion of the Florida Everglades by the spotted tilapia, Tilapia mariae

South Florida has the highest number of naturalized freshwater fish species in the world.  How these affect the local native fish populations, however, is largely unknown. In particular, native sunfish of the family Centrarchidae are important as predators in structuring fish assemblages and are economically valued as game fish. Spotted tilapia, Tilapia mariae, a successful West African invader, exhibits territorial and spawning behavior that closely matches that of native sunfish. We tested the hypothesis that the sunfish and tilapia would compete when space was limiting. Additionally, we predicted that T. mariae, because of its high aggressiveness, would be more successful in acquiring space. We collected individuals of both groups from Big Cypress National Preserve, Everglades National Park, and the South Florida Water Management District canal system for laboratory trials in which individual territories were invaded by a member from the other group to determine potential competitive interactions. Tilapia residents were more aggressive than sunfish, responding more quickly to intruders and with higher numbers of attacks. Tilapia resisted all invaders, but 30% of sunfish residents were ejected. We surmise that this behavior is an important component in the success of T. mariae in South Florida and has the potential to affect the quality of spawning habitat available for native sunfish.