High Predation Pressure by an Introduced Flatworm on Land Snails on the Oceanic Ogasawara Islands 1

The introduction of a predatory flatworm, Platydemus manokwari , has been considered a cause of the decline of endemic land snails on the tropical oceanic islands. To clarify the effect of P . manokwari on land snail survival in the field, we examined survival rates of snails experimentally placed in areas where snails are absent ( i.e ., P . manokwari is present) on Chichijima, Ogasawara (Bonin) Islands. We found that over 50 and 90 percent of the snails were dead after 3 and 11 d, respectively, and that the main cause of mortality was predation by P . manokwari .