Dispersal is fundamental to biogeography and the evolution of biodiversity on oceanic islands

Abstract

Vicariance biogeography emerged several decades ago from the fusion of cladistics and plate tectonics, and quickly came to dominate historical biogeography. The field has since been largely constrained by the notion that only processes of vicariance and not dispersal offer testable patterns and refutable hypotheses, dispersal being a random process essentially adding only noise to a vicariant system. A consequence of this thinking seems to have been a focus on the biogeography of continents and continental islands, considering the biogeography of oceanic islands less worthy of scientific attention because, being dependent on stochastic dispersal, it was uninteresting. However, the importance of dispersal is increasingly being recognized, and here we stress its fundamental role in the generation of biodiversity on oceanic islands that have been created in situ, never connected to larger land masses. Historical dispersal patterns resulting in modern distributions, once considered unknowable, are now being revealed in many plant and animal taxa, in large part through the analysis of polymorphic molecular markers. We emphasize the profound evolutionary insights that oceanic island biodiversity has provided, and the fact that, although small in area, oceanic islands harbour disproportionately high biodiversity and numbers of endemic taxa. We further stress the importance of continuing research on mechanisms generating oceanic island biodiversity, especially detection of general, non‐random patterns of dispersal, and hence the need to acknowledge oceanic dispersal as significant and worthy of research.