Interference competition driven by hydric stress in Korean hylids

Competition is based on the type and importance of the resource sought, and interactions intensify with the importance of a given resource. One of the highest degrees of interference competition is physical interactions for a given resource. The treefrogs Dryophytes japonicus and D. Suweonensis compete for spatial resources for the production of advertisement calls. Here, we have investigated a case of direct interference competition due to artificial hydric stress caused by variations in the irrigation system of rice paddies. Under this specific condition, an unusually high number of males of both species congregated in a single flooded field. We first found that males segregated following a demonstrated pattern, with D. Japonicus on the edges and D. Suweonensis at the centre of the submerged field. However, the differences in the distance to the edge of the submerged field for amplexuses of the two species were not significantly different. Due to the high number of individuals and the small size of the site, the area used by males of both species partly overlapped, and thus lead to physical interactions between two males of the two species. Dryophytes japonicus took over a calling site and managed to remove the opponent male. We sequentially described the interaction here, potentially representative of the general outcome of interference competition between these two species.