Sugita, N., Emura, N., Ueda, K. In Pacific archipelagos, pigeons that can disperse large seeds have been greatly reduced or extinct, so that flying-foxes play an unique role in longer-distance dispersal of the large-seeded fruits e.g. pandanus (ca. 70 mm). Its effectiveness of seed dispersal depends on their population density. In the Ogasawara Islands, two native pigeons are extinct and decreasing, and Bonin flying-foxes Pteropus pselaphon survive. An alien species Black rats Rattus rattus has an impact on ecosystems of indigenous flora and fauna by predation. Bonin flying-foxes carry intact seeds of Pandanus boninensis in mouth but Black rats gnaw a hole in fruits and crunch seeds. We investigated the relationship between the flying-foxes and pandanus, and estimated the impact of rats on native species interaction. We counted the number of pandanus fruits and feeding marks by rats. To test whether the flying-foxes are the effective disperser of native large fruits or not, we observed their feeding behavior by IR video cameras. Pandanus plants (30.2–70.4%) suffered from any rat predation. Flying-foxes ate solely fruits and dropped it beneath the parent tree. Our results suggested that the flying-foxes would lose opportunities to disperse large seeds because of the seed predation by rats, the population decline of flying-foxes and their food habitat shift.