Biogeography and phylogeography
Biogeography is the study of the patterns and causes of the distribution of living things. There are a range of approaches to answering biogeographical questions, including historical biogeography, ecological biogeography and phylogeography.
Major historical factors that influence current distributions include vicariance and dispersal. Vicariance is the splitting of distributions, such as when ancient landmasses split and separate due to continental drift, or when mountain ranges divide lowland populations. Dispersal is movement of organisms or their propagules (such as seeds). The relative contribution of vicariance and dispersal to current plant distributions is much debated.
Phylogeography is the study of the genetic and geographic structure of populations and species. Phylogeography generally uses genetic information to examine genealogical history and patterning within species and populations. This information is used to infer relationships of biogeographic areas and species histories. The genetic markers utilised are often uniparentally inherited, such as mitochondrial or chloroplast DNA sequences, and as such they track the genealogical history of either the maternal or paternal line; in plants this is the pollen (male) or seed (female) parent.
Genetic discontinuities associated with large geographical gaps between taxa and populations, such as inter-continental breaks, have been relatively well studied. However, as our knowledge of the Australian biota improves, it is becoming clear that strong genetic structure also often exists on a more local scale, such as either side of geographic features. For example, the Hunter Valley in New South Wales or the Black Mountain Corridor in Queensland form genetic breaks in a number of animal taxa. These geographic barriers and landscape features have acted as important filters for evolution.
For plants the situation is less clear. This is perhaps largely the result of limitations in the available genetic markers. In the animal world, mitochondrial DNA sequences have proven extremely useful. Overall, it remains unclear where significant genetic disjunctions occur in plant taxa distributions, particularly in south-eastern Australia.
Biogeography and phylogeography at Royal Botanic Gardens Melbourne
At Royal Botanic Gardens (RBG) Melbourne, Frank Udovicic and collaborators are investigating the phylogeography of Eucalyptus deglupta ; one of the few eucalypt species not native to Australia. Gillian Brown is carrying out detailed research on the population genetics of the putative sister taxon to Acacia, Paraserianthes lophantha. David Cantrill and a team of researchers are testing hypotheses about biogeographic links between New Caledonia and Australia, using plants from the family Rutaceae. Insights on the origin of the Australian flora are being gained from a collaborative project on Persoonia, involving Gareth Holmes, Daniel Murphy and David Cantrill.