It was curiosity about the reasons for Tasmanian devils’ low genetic diversity, a characteristic that was often noted but never fully explained in many of the papers she was reading, that prompted University of Tasmania PhD candidate Anna Brüniche-Olsen to discover why. The results of her study, the first to provide a ‘quantitative assessment of devil population size changes through time’ were published recently in Biology Letters.
Brüniche-Olsen and her team analysed available microsatellite data from 10 different locations across Tasmania to estimate the stability of devil populations over time, and they found evidence of declines that pre-date the fatal facial tumour disease that is currently ravaging the devils’ wild populations.
The results show four major events are likely to have influenced the current population distribution and low genetic diversity of Tasmanian devils. Environmental change around the last glacial maximum approximately 20,000 years ago was responsible for the first decline. The resulting drier colder climate, and the comparatively sparse scrublands and grasslands that replaced rainforest habitat, would have impacted on the availability of prey, and suitable denning habitat. Increased El Nino-Southern Oscillation activity 3000-5000 years ago caused the second major decline. ENSO brought more climate instability, that again led to arid conditions and periods of drought, and a subsequent reduction in the abundance of prey, and favourable habitat.
The arrival of Europeans 200 years ago, and the extensive bounty hunting of devils and thylacines that followed, triggered the third decline, while DFTD is responsible for the current, fourth decline.
“We took samples of devil populations from various sites across Tasmania from 2004 and tried to figure out the demographic history of the species from those. But we also had samples from the 1960s, which were quite interesting because they were from Mt William, the place where DFTD was first found, and given that this was around 30 years earlier, we could use those to test what had happened before. We found evidence of declines, and we timed it and put up four hypotheses for why the declines had happened,” Brünich-Olsen said.
Their lower genetic diversity increases devils’ vulnerability in today’s changing climate conditions, an important factor for the species’ future survival.
“In relation to climate change devils seem to be quite prone to changes, it seems to be one of their main drivers of population size and we suspect that when the climate changes in the future we might see further declines, both for the devil and for other species.”
A companion study she completed last year looked at the potential impact DFTD was having on genetic diversity. The results from samples taken from across the state over a seven year period between 1999-2006 found that while the disease did not directly impact on genetic diversity, it did affect the animals’ migration patterns, showing devils tended to migrate to areas with lower population density as the disease spread across the state.
The impact of a changing climate on other species will be the focus of Brüniche-Olsen’s next study.
Anne Layton-Bennett