Evolutionary Analysis of the Generation and Loss of Biodiversity

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Gillespie 9726573 We are undertaking part of a large study examining the dynamic nature of ecological and geographic range occupation by species. The ultimate goal is to determine whether, and how, evolutionary history dictates the size of a species range, and hence its vulnerability to extinction. The focus of the research is a large and diverse species radiation of spiders endemic to the Hawaiian Islands. The current objectives are: (1) to resolve the evolutionary relationships among 4 groups of the spiders, two of which differentiate extensively within islands, while the others differentiate primarily between islands or mountains; and (2) for a single group, to generate estimates of effective population size and gene flow (using molecular markers) between populations of each species. If it were possible to determine the natural evolutionary changes in distribution among species through their evolutionary history, then it may be possible to distinguish species that are naturally restricted in their range from those that have been confined due to human impact. The objective of the proposed study is to understand relationships among populations and species, so that we will be able to go on to test whether the natural evolutionary future of a species can be predicted. We have argued that, for species characterized by extensive migration, local subdivision of populations will be impossible. Therefore, species divergence can only occur when a population becomes isolated, for example when it reaches a new land mass, at which time the new species is also likely to expand in abundance and range. In such a scenario, the most recently formed representative of a species group will be the most widespread, while the older species in that lineage will be more restricted and vulnerable to extinction. For species exhibiting reduced migration, local population subdivision should be possible, with subdivided species becoming more restricted in abundance and range. In this second scenario the more recently derived species should be the most restricted and vulnerable to natural extinction. The data generated in this study will indicate how information on phylogenetic relationships among clades can be most effectively coupled with data on effective population size and gene flow between populations in order to statistically test for significant patterns of distributional change.