Meeting Abstract
The General Dynamic Model (GDM) of oceanic island biogeography extends the predictions of MacArthur and Wilson’s dynamic equilibrium model of island biogeography by incorporating geological timescales and the effects of island ontogeny on species diversity. Many of the predictions of the GDM have found support in recent studies of volcanic archipelagos, but this work tends to ignore the morphological diversity of these lineages. We use the spectacular radiation of Galápagos endemic land snails of the genus Naesiotus to test several GDM predictions of morphological diversity through island ontogeny. In general, we find support for the GDM in the patterns of Naesiotus diversity across Galápagos. In particular, species diversity exhibits the characteristic hump-shaped curve through island ontogeny, with middle-age islands containing the greatest species diversity. In contrast, we find that morphological diversity (i.e. the volume of the morphospace occupied by all the species on a given island) continues to increase as islands age. However, the density of island morphospace becomes increasingly depauperate over time, such that species on older islands tend to be more different from one another than species on younger islands. These results are exciting because they support predictions of the GDM for morphological diversity in that older islands, lacking much of the topographical complexity of middle-age islands, are less able to support many ecologically and morphologically similar species. Instead, as islands age, morphologically unique species may be the last to disappear before the islands themselves submerge.
