A Field Guide to the Snails of Lord Howe Island

10 Origins and diversification The species richness of land snails on Lord Howe Island is unparalleled by any other region of comparable size in Australia and arguably the world. We are only just beginning to understand how and when this astonishing diversity of land snails has emerged. The endemic species of Lord Howe Island, which are found nowhere else in the world, must have evolved on the island from ancestors that arrived here long ago, but are now extinct. As unlikely it may seem, the ancestral species that gave rise to the present day diversity probably arrived on Lord Howe Island from Australia or New Zealand, after being carried across the ocean by massive storms, stuck to the plumage of birds, or rafting on large pieces of driftwood. As speciation is a slow process, the first land snails must have arrived on the island soon after its formation more than 6 million years ago. Several of these ancestral species have since radiated into flocks of species, each occupying a slightly different ecological niche. For example, the diplommatinids on Lord Howe have evolved into different size classes. Minute, medium-sized and large diplommatinids are able to coexist with each other, avoiding competition for their preferred source of food. The diversity of available habitats has also played an important role in facilitating species diversity. As species gradually adapted to live in certain microhabitats, such as leaf litter, rock crevices, or palm leaves, they also diversified over time. Last but not least, the geological variety of the island was another important driver of diversification. The environmental conditions (climate, vegetation) of the mountain peaks are so different from those of the lowlands that high altitude specialists have evolved in many land snail groups, which exclusively inhabit the summits of the southern mountains. However, not all land snails can look back on an ancient history on the island. Instead, some have arrived here comparatively late, usually aided by human activities. Among these recent arrivals is one species that is native to New South Wales, the Sydney Copper Wheel Snail, and several worldwide tramp species, which now have nearly global distributions thanks to human assistance. There are twelve species of these pests of mainly European and North American origin on Lord Howe today. The effects of the introduced species on native species are currently unclear.