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Evolutionary Biology of the Australian Wet Tropics

Molecular evidence supports the contention that historical contraction and expansion of the Australian Wet Tropics (AWT) rainforest has affected species distributions and diversification, but also provides qualitative evidence for differences among species in the temporal and spatial scale of their responses. We combine ecological, GIS and molecular methods to examine the spatial history of amphibian and reptile species endemic to the biologically diverse and intensively studied rainforests of the Australian Wet Tropics. Our long-term aim for this system is to understand how changes in rainforest distribution have influenced speciation and adaptive divergence (Moritz et al. 2000; Moritz 2002) and how these processes, along with local extinction, recolonisation and species interactions shape patterns of community diversity (Williams et al. 1996, Williams 1997, Williams & Pearson 1997, Williams & Hero 2001, Schneider & Williams in press). Our research to date has documented patterns of community diversity and comparative phylogeography. Phylogeographic studies of rainforest-restricted fauna in the AWT frequently reveal spatially congruent clade distributions and secondary contact zones (Joseph et al. 1995; Schneider et al. 1998), offering strong qualitative agreement with the locations of historical refugia and predicted areas of range expansion events in climatic paleomodelling (Hugall et al. 2002). However, levels of observed (net) sequence divergence across shared biogeographic barriers (eg. the Black Mountain Barrier) vary widely even within a genus and several species show additional genetic breaks across large river drainages (eg. Bloomfield, Tully). A major aim of our current research is to understand how and why species vary in their responses to a common history of rainforest fluctuation. It is clear that more precise and spatially explicit estimates of population history across co-distributed species are needed. Further, we need to integrate the molecular analyses with information on relevant ecological attributes of each species if we are to predict and understand their responses to spatial models of past and future habitat change.

Our current approach combines multi-locus estimates of population history with spatially explicit models of habitat distributions under varying climates and with field-derived estimates of habitat specialization and climate “niche” breadth. Novel aspects of the research include the following: 1) We will apply multilocus coalescent methods to infer population divergence, size(s) and migration rates across multiple codistributed species in a system with a well-known history of habitat fluctuations. Multilocus approaches have not previously been applied to comparative biogeography on this scale. 2) We will develop explicit spatial models of historical distributions of species by combining the molecular evidence with paleodistribution models that incorporate information on climate-driven changes in habitat distributions, conditioned on observed environmental niche breadth and dispersal limitation. 3) By combining the models of individual species, we will generate spatial models of assemblage structure through the climatic fluctuations of the late Quaternary. 4) We will use our knowledge of sensitivity of species to historical climate change to improve predictions about the impacts that future climate change on potential ranges of these species.




Craig Moritz Research Group - Home

Museum of Vertebrate Zoology
Department of Integrative Biology
University of California, Berkeley