The potential tropical island distribution of a temperate invasive snail, Oxychilus alliarius, modeled on its distribution in Hawaii

Oceanic islands typically have very high levels of indigenous snail biodiversity when compared with continental land masses. The predatory snail Oxychilus alliarius, which has already been introduced to many places around the world, including some island groups, may have the potential to cause major declines in indigenous snails where it is established. Here we present the four best of 36 models that use O. alliarius presence and absence data from the Hawaiian Islands of Maui and Hawaii to estimate habitat suitability on the six largest Hawaiian Islands, validating the estimates based on known distributions of O. alliarius on the other four islands (Molokai, Lanai, Oahu and Kauai). These models were further validated with data from four other islands around the world to which O. alliarius has been introduced. They were then applied to 31 tropical and subtropical islands and island groups around the world, on which O. alliarius has not been recorded, to predict the extent of suitable habitat on those islands and thus the potential for O. alliarius establishment should it be introduced. The results showed that there are islands with suitable O. alliarius habitat in the Pacific, Indian and Atlantic Oceans, and in the Caribbean Sea, and that the four models make slightly different predictions based on which environmental variables they use. The models indicate that there is still a large amount of area on islands supporting indigenous snail species that is suitable for establishment of O. alliarius.