Resource competition and coexistence between alien and domestic turtles in relation to diving behaviour

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I investigated diving behaviour of alien turtles, Trachemys scripta, and domestic turtles, Chinemys reevesii, to know how inter-species competition occurs between these species and whether these species can coexist. The study using data-loggers which record diving depth revealed that T. scripta of large size used water column more frequently than that of small size, indicating that this species depends on water area in younger stage, whereas C. reevesii of large size used water column less frequently than that of small size, indicating that this species depends on water area in older stage. When alien and domestic turtles use water column at the same time, young alien species used water column more frequently than that using water column without other species, whereas older alien species used water column less frequently that that using water column without other species. On the other hand, younger domestic turtles with alien species used water column less frequently than without alien species, whereas older domestic turtles used water column more frequently with alien species. These findings suggest that the effect of alien species on domestic turtles depends on the size of the turtle, which is supposed to be related with age. That is, when domestic turtles are small and young, competition between the domestic and alien turtles should be hard for the domestic species to survive and will be excluded. However, when domestic turtles are large and old, the competition should not be very hard to survive and the alien species will be excluded. Since it is hard for domestic turtles in younger stage to be dominant against alien species, the management of alien turtles is necessary for conservation of domestic turtles.