Abstract
Island systems generally have fewer species than continental areas due to their small size and geographical isolation. Low island diversity reduces the possibility of exportation of island lineages and island systems are not thought to have a major influence on the build-up of continental diversity. However, the view that islands represent the end of the colonization road has recently been challenged and islands do represent the origin of some specific continental lineages. Here we assess the net contribution of island systems to global diversity patterns of passerine birds, using a complete phylogeny (5,949 species), biogeographical regionalization and null-model comparisons. We show that, in contrast to major continental regions, island regions export relatively more evolutionary lineages than would be expected based on current distributional patterns. This result challenges a central paradigm in island biogeography and changes our perception of the relative importance of islands for the build-up of global diversity.
Highlights
Island systems generally have fewer species than continental areas due to their small size and geographical isolation
We use complete global distributional[12] and phylogenetic data[13] for passerine birds (5,949 species), biogeographical regionalizations, ancestral state reconstructions and a nullmodel-based analytical approach to examine the spatial dynamics of species distributions with a particular emphasis on the exchange of evolutionary lineages between biogeographical regions and the relative role of continental versus insular regions in contributing to global diversity
We show that islands contribute to continental diversity and contribute relatively more to global diversity than expected based on the current distributions of passerine species
Summary
Island systems generally have fewer species than continental areas due to their small size and geographical isolation. In contrast to major continental regions, island regions export relatively more evolutionary lineages than would be expected based on current distributional patterns This result challenges a central paradigm in island biogeography and changes our perception of the relative importance of islands for the build-up of global diversity. Today the focus on island systems as model systems for ecological and evolutionary research is stronger than ever[6] despite the common assumption that insular faunas are depauperate and stem from a simple one-way, downstream flow of colonists from continents[4,5,7,8] This assumption has been challenged recently in a series of studies demonstrating that islands may in some cases represent sources for continental diversity[9,10,11]. We show that islands contribute to continental diversity and contribute relatively more to global diversity than expected based on the current distributions of passerine species
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