Evolution and Extinction of Land Snails on Oceanic Islands

Nonmarine molluscs are the major animal group with the greatest number of recorded extinctions due to anthropogenic impacts, and that number is certainly a serious underestimate. Land snails, particularly endemic land snails of oceanic islands, are the group of molluscs that have sustained the most extinctions. Understanding their ecology and the evolutionary processes that have led to their extreme vulnerability is crucial if we are to be able to conserve these diverse and important species. Oceanic island snails tend to have low α-diversity and high β-diversity, and divergence of habitat use among related species is known to occur in some radiations of land snails on oceanic islands. Processes of speciation and ecological interaction are possible major drivers of these patterns. The ecological opportunities available at the initial stage of insular evolution and the scarcity of effective predators may have led to divergence of habitat use and high β-diversity in oceanic island snails. Fewer and less diverse predators on oceanic islands lead to the evolution of fewer and less diverse defense traits in oceanic island snails, which results in their high vulnerability to non-native predators. High β-diversity of oceanic island snails also results in great vulnerability to habitat loss. Accordingly, the high susceptibility of oceanic island snails to extinction reflects their evolutionary history.