No place to go and nowhere to be?: Characterising demography of the southern scrub-robin (Drymodes brunneopygia) using molecular and modelling tools for conservation.

In Australia anthropogenic development has resulted in substantial loss and modification of natural habitats. This development has occurred most intensively around the continent’s southern and eastern coastal areas where fertile soils and climates appropriate for agriculture are located. Consequently, a diverse range of species found within this region frequently suffer from fragmented distributions that alter evolutionary processes and result in increased population structure and the erosion of genetic diversity. Augmenting the effect of habitat clearing and alteration, climate change is predicted to result in increasing temperature and decreasing rainfall in many regions of Australia. What makes anthropogenic climate change a major threat is that its impact will occur in ecosystems already suffering fragmentation and other perturbations associated with human activity. This thesis seeks to characterise the molecular demography of the ground-dwelling southern scrubrobin (Drymodes brunneopygia), a species whose future is at risk from both habitat loss and climate change. I begin by reviewing the current use and potential role of molecular demography to inform species distribution modelling for conservation. My study of the southern scrub-robin itself begins with the development of microsatellites. Employing these microsatellites, I investigate genetic diversity and recent migration across intact and fragmented mallee vegetation in southern Australia. Our assessment of habitat protection for this species reveals that large areas of contiguous native vegetation are most often conserved toward the climatically extreme, northern distribution of the southern scrub-robin. Conversely, we find that genetic diversity and larger effective population size are concentrated in southern regions, which are dominated by agriculture. Subsequently I investigate the composition and structure of different mallee understorey vegetation types, and the nature of their resources and risks to dispersing southern scrub-robins in both the historic (pre-clearing) and contemporary landscapes. Landscape types with an open or inaccessible understorey were shown to increase population genetic structure in the southern scrub-robin, in particular chenopod habitat. Conversely, landscape types that offered a dense, accessible understorey structure decreased genetic structuring, possibly due to increased predator protection and foraging opportunities during dispersal. I proceed by investigating the relationship between genetic diversity and habitat quality at southern scrub-robin home sites. Genetic diversity was diminished by the presence of feral predators and weed infestations, suggesting the control of invasive species should be a conservation priority for the southern scrub-robin. I also confirm the fundamental requirement of a dense shrubby understorey for this species, suggesting that control of feral herbivores may also be of conservation benefit. Finally, I consider the role that adaptation to change can play in securing the future of the southern scrub-robin in an era of habitat loss and climate change. Simultaneously considering the effects of distance and the environment, I identify substrate and temperature conditions among the most important environmental variables associated with spatial patterns of genetic diversity. To prioritise regions for additional conservation actions, I consider predicted genetic uniqueness, land use, current and future habitat suitability and the amount of pressure existing genetic-climate relationships are expected to experience.Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 201