School of Botany - Theses
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ItemThe intersection of ecology and evolution: a case study of Eucalyptus in the Grampians Ranges, Australia( 2011)This thesis explores the ecology and evolution of Eucalyptus species in the Grampians ranges, Australia. The Grampians ranges are an ancient isolated collection of three ranges with steep habitat gradients relative to the surrounding homogeneous landscape. This region is a local centre of species diversity and endemism, in which many closely related species interact. I use a range of approaches to understand the ecological and evolutionary history of contemporary patterns of species distribution, traits, and co-occurrence. First, I investigate speciation and gene flow for a clade of Eucalyptus endemic to high elevation rocky outcrops in the Grampians. I document chloroplast DNA structure for the three high elevation species (E. serraensis, E. verrucata, and E. victoriana) and a neighbouring species E. baxteri, which surrounds endemic populations. I found generally high chloroplast diversity, local genetic structuring, and local interspecific gene-sharing. Second, I broaden the scope to include all 20 Eucalyptus species in the region. I am generally interested in relations between species, functional traits, and environments. I model the distribution of species across environmental gradients using a modern niche modelling technique. I incorporate species interaction terms and model groups of species across a taxonomic hierarchy to explore species and clade interactions. Using a subset of variables found to be important in niche models, I then used a hierarchical modelling approach that describes how species responses to environmental variables change as a function of their traits. I used traits from the leaf-height-seed strategy scheme (specific leaf area (SLA), maximum height and seed mass). I found a range of important trait-habitat associations. For example, SLA modified species responses to rock cover such that thicker, denser leaves were found on rocky areas with less soil. Seed mass was associated with edaphic variables such as valley bottom flatness and soil texture. Maximum height of species increased with solar radiation and rainfall. Third, I explored the evolutionary history of these trait-habitat associations with phylogenetically independent contrasts using a phylogeny and niche model estimates. I found a general progression from early divergence of seed mass-edaphic associations to late divergence of height-climatic associations. SLA diverged early with edaphic associations and later with climatic associations. I interpret the early edaphic- late climatic- associations divergences with the paleoclimatic and geologic processes of the Grampians region. Finally, I again explore trait, niches, and phylogenetic relationship, this time in the context of local species assemblages. I address the longstanding observation that within large genera, closely related species do not co-occur in local neighborhoods. I find that habitat drives species assemblages except when species interbreed. I attribute the lack of co-occurrence of reproductively compatible species to reproductive interference via hybridization and introgression. Results from the initial genetics study confirm the importance of geneflow for these species. This approach describes a genetic mechanism underlying an ecological pattern and provides a cohesive story of the ecology and evolution of Eucalyptus in this region.