Juvenile invasive red-eared slider turtles negatively impact the growth of native turtles: Implications for global freshwater turtle populations

Invasive species are a significant cause of biodiversity declines on a global scale with novel species interactions often causing ecological damage through predation or competition. Red-eared slider turtles (Trachemys scripta elegans) have been introduced to wetlands throughout the world and have negatively impacted native species, particularly other species of turtles. In our controlled feeding experiments in mesocosms juvenile red-eared slider turtles negatively impacted the growth of juvenile red-bellied turtles (Pseudemys rubriventris), an IUCN near threatened species and a Pennsylvania threatened species, through exploitative competition for limited food. In mixed species experimental treatments, in which food resources were abundant, juvenile red-bellied turtles grew significantly faster and ate more food than juvenile red-eared slider turtles. In mixed species experimental treatments, in which food resources were limited, red-eared slider turtles ingested more food, gained mass faster, and maintained body condition while red-bellied turtles lost body condition. There were significant differences in growth rates seen between resource availability regimes. In treatments in which resources were abundant there were no significant differences between turtles housed in mixed species or single species groups. In limited resource treatments red-bellied turtle body condition was significantly different between single and mixed species groups while there were significant differences in mass and body condition for red-eared slider turtles. Our results suggest that one mechanism by which red-eared slider turtles detrimentally impact ecologically similar species is through competition for limited food resources. We hypothesize that growth of red-eared slider turtle populations will lead to population declines of native turtle species throughout their introduced ranges because they use limited food resources more efficiently for their growth and development than native species.