A Tale of Two Islands: Long Distance Dispersal to Oceanic Islands and the Influence of Dispersal Potential on Large-Scale Phylogeographic Patterns

Abstract

Comparative phylogeography seeks to compare phylogeographic patterns of multiple co-distributed species in order to examine levels of temporal and spatial congruence. Comparative assessments can lead to reconstructions of major trends in the recent histories of dispersal of a region and can provide significant advances in understanding how behaviour, demography and natural histories of species and populations can influence phylogeographic patterns. When common spatial patterns of evolutionary sub-division are found between co-distributed species they are thought to share a biogeographic history. Although concordant phylogeographic patterns have been found across multiple taxa, not all comparative phylogeographic studies have found evidence of congruence. The influence of dispersal potential on the phylogeographic structuring of multiple co-distributed species was the main focus of this thesis. The main goal was to explore how dispersal potential, based on life history characteristics, influenced phylogeographic structure on a large-scale in multiple co-distributed species, and in particular how this influenced oceanic island populations. Whilst there are disagreements in the biogeographic literature as to whether vicariant or dispersal processes best explain the geographic distribution of a species, the colonisation and accumulation of biotic assemblages on oceanic islands is unequivocally the result of transoceanic dispersal. The biotic communities present on oceanic islands therefore inevitably consist of species that are able to disperse well. Genetic variation within island populations is directly influenced by the dispersal potential of the species in question. Species that disperse frequently will be more closely related to the source population due to continual migration to the islands from mainland (or other island) sources; whereas species that do not disperse as often will be more genetically distinct and divergent from the source population.