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

我调查了外来海龟Trachemys Scripta和家龟Chinemys reevesii的潜水行为，以了解这些物种之间如何发生物种间的竞争，以及这些物种是否可以共存。利用记录潜水深度的数据记录仪进行的研究表明，大体型的刺参使用水柱的频率高于小体型，这表明该物种在幼龄阶段对水域的依赖程度较高，而大体型的乌贼使用水柱的频率低于小体型的水柱，表明该物种在老年阶段对水域的依赖程度较高。当外来龟和家龟同时使用水柱时，幼龄外来物种使用水柱的频率高于不使用其他物种的水柱，而年长的外来物种使用水柱的频率低于不使用其他物种的水柱。另一方面，有外来物种的年轻家龟使用水柱的频率低于没有外来物种的家龟，而有外来物种的年长家龟使用水柱的频率更高。这些发现表明，外来物种对家龟的影响取决于海龟的大小，这被认为与年龄有关。也就是说，在家龟小而幼的情况下，家龟和外来龟之间的竞争应该会使国内物种难以生存，并将被排除在外。然而，当国内的海龟又大又老的时候，竞争应该不会很难生存，外来物种将被排除在外。由于幼龄家龟很难对外来物种占优势，因此对外来海龟的管理是保护家龟的必要手段。

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.