Morphological and ecological shifts in a land snail caused by the impact of an introduced predator

Introduced predators have become major threats to native animal species in oceanic islands. A number of studies have shown that alien predators have caused serious extinctions of island endemics. However, little attention has been paid to the evolutionary impacts of alien predators on native species. The present study shows that predation by black rats, Rattus rattushas resulted in ecological and morphological changes in the land snail Mandarina anijimanafrom the island of Anijima in the Ogasawara archipelago. The frequency of empty predated shells has increased over the past 17-19 years in southern areas of the island. The shells of these snails were found to be significantly higher, smaller and darker in the survey in 2006 than in the survey in 1987-1989 performed in central and southern parts of Anijima, where predation by Rattuswas serious. M. anijimanawere formerly restricted to shallow broad-leaved litter, whereas they are currently found in deep palm litter, where predation pressure from Rattusmay be lower. This suggests that increased predation pressure by Rattushas changed the habitat use of M. anijimana.The close association between shell morphology and habitat use of Mandarinaspecies suggests that the habitat shift induced by the predation of Rattushas caused these changes in the shell morphology of M. anijimanaover a period of 17-19 years. Reprinted from Chiba S (2007) Ecological Research 22:884-891, with permission of the Ecological Society of Japan.