Invertebrate invasions on Pacific islands and the replacement of unique native faunas: a synthesis of the land and freshwater snails

The once immense diversity of native Pacific island land snail species, with high single island or archipelago endemism, is declining dramatically. The native/endemic species are being replaced by a much smaller number of widespread tropical 'tramps', that is, those species that are most readily transported by humans. The 82 introduced (including 14 `cryptogenic') land snail species recorded include some that were distributed accidentally by Pacific islanders before European exploration of the Pacific and that are now widespread. However, the majority are modern introductions, with many recent accidental introductions often associated with the horticultural trade. Native freshwater faunas were less diverse than the terrestrial faunas and exhibited much lower endemism. Among the 59 alien freshwater species recorded (including 38 `cryptogenic' species), the most diverse and widespread are the thiarids.