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Title: Investigating plant diversity in Mediterranean climates
Author: Yesson, Christopher
ISNI:       0000 0001 3575 1080
Awarding Body: University of Reading
Current Institution: University of Reading
Date of Award: 2008
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The mediterranean-type climate zones, typified by hot-dry summers and coldwet winters, are remarkable for their botanical richness. These areas developed through parallel processes of aridification 15-10 million years ago and present a unique opportunity to study how plant groups have reacted to climate change. This thesis investigates the evolutionary impact of palaeoclimatic changes in these. winter-wet biomes, and asks whether similar patterns of diversity are repeated in each of these biomes. The following questions are critical to this study: Can the evolutionary impact of climate change be detected using phylogenetic inference and niche modelling? Are climatic niches conserved? Can we reconstruct ancestral niches and so estimate ancestral areas? And what data are available for such studies? These questions are explored using exemplar plant genera, each of which show diversification within a mediterranean-type biome. These are: Drosera (Droseraceae), which shows greatest diversity in SW Australia; Cyclamen (Myrsinaceae) from the Mediterranean basin; Pelargonium (Geraniaceae), centered in the South Africa cape; and Gastrolobium (Fabaceae), an Australian endemic primarily from the Southwest. This study describes and develops the techniques of 'phyloclimatic modelling', a combination of bioclimatic niche modelling and phylogenetics. Phyloclimatic modelling reconstructs ancestral niches over a phylogeny. Molecular dating of the phylogeny produces age estimates for evolutionary divergences, permitting examination of the reconstructed ancestral niches within palaeoclimate models of the time of the ancestral lineage. Such analysis permits geographic exploration of climatically suitable areas and so provides estimates of ancestral areas. These techniques rely upon large amounts of high quality distribution data. There is a rapidly-increasing wealth of on-line biodiversity information available. These data, particularly that concerned with distribution data, should be treated with caution, and wherever possible, independently validated before use. If used appropriately, these data can be a valuable resource. The major diversification of each of the four groups occurred during or shortly after the development of the winter-wet biomes. They demonstrate clear patterns of phylogenetic conservancy for many climatic parameters, notably for those of seasonal rainfall. Similar patterns are found for bioclimatic niche models, which are shown to be conservative over evolutionary timescales. Those groupS demonstrating current diversity within winter-wet biomes had an ancestral preference for the seasonal Mediterranean climates characterised by dry summers and wet winters. These ancestral niches, when examined within palaeoclimate reconstructions for the Miocene, show that each group would have found climatically suitable areas close to their present-day distributions. Phyloclimatic modelling produces a valuable insight into the evolutionary impact of climate change. There is a detectable footprint of climate change on many phylogenies. The emergence of the winter-wet biomes created an opportunity for species' diversification. This evolutionary diversification was not a rapid response to climate change, but has been a continual process occurring in zones with a prolonged period of climatic stability. It appears that the stable environment permitted gradual diversification probably triggered by local ecological or geological processes. This has major implications in light of the present rapidly changing climate.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available