Predator or disperser? A test of indigenous fruit preference of alien rats (Rattus rattus) on Nishi-jima (Ogasawara Islands)

Abstract

The Black Rat Rattus rattus has invaded many of the Ogasawara Islands, including Nishi-jima. To evaluate the effects of this alien rat on fruits in Nishi-jima, I set out 1 772 fruits of five indigenous tree species and tracked them for two months by locating attached long-labelled lines. The rats consumed more than 95% of the small Neolitsea sericea var. aurata and Livistona boninensis fruits. For larger fruits, rats consumed 48.3% of Pandanus boninensis, 11.2% of Terminalia catappa, and 64.4% of Ochrosia nakaiana. Larger fruits were carried further than small fruits, however, the ratio of survival to frugivory decreased with increasing distance carried in all species. The role of Rattus rattus as seed disperser is limited, and its fruglvory impact is more serious for trees producing small fruits.