Enhanced interspecific territoriality and the invasion success of the spotted tilapia (Tilapia mariae) in South Florida

Abstract

South Florida’s freshwaters are amongst the most invaded in the world with 34 naturalized fish species. How these non-natives affect the local native fish populations, however, is largely unknown. Native sunfish of the genus Lepomis are important as predators in structuring fish and invertebrate assemblages in the swamps and seasonal wet prairies of the Big Cypress Swamp and Florida Everglades. The spotted tilapia, Tilapia mariae, is a successful West African invader that exhibits territorial and spawning behavior that closely matches that of native Lepomis sunfishes. We tested the hypothesis that Lepomis sunfishes and T. mariae would compete when space was limiting. Additionally, we predicted that T. mariae, because of their aggressiveness, would be more successful in acquiring space. We collected juveniles 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 likely competitive interactions were staged and observed. T. mariae were bolder and more aggressive than Lepomis sunfishes. T. mariae residents resisted all intruders whereas 30% of Lepomis sunfish residents were ejected. We surmise that these enhanced behaviors of T. mariae are an important component of their success in South Florida. The continued spread of T. mariae populations throughout South Florida into natural habitats suggests an increasing potential to affect the quality of spawning habitat available for Lepomis sunfishes and warrants a renewed focus on T. mariae as a non-native species of special concern.