SER in the News
Raising fears of killer combo
By Simon Bevilacqua
09 October 2005
THE cancer killing Tasmanian devils is unlikely to cause the species' extinction on its own, says a new study. But the disease could combine with other threats such as road kill, persecution and competition from introduced species to see the demise of the state's icon species.
Interstate research suggests the spread of devil facial tumour disease (DFTD) could halt when devil numbers become low enough to affect transmission.
A study by researchers Corey Bradshaw and Barry Brook of the Northern Territory's Charles Darwin University found DFTD would probably not wipe out the species.
"The recent appearance and rapid spread of a debilitating and usually lethal cancer-like disease has raised concerns regarding the species' future," the study's report said.
"We used a demographic-matrix modelling approach to evaluate the potential long-term implications of epidemics.
"The study found that large fluctuations in abundancy resulted when DFTD outbreaks were density dependent.
"This resulted in a low probability of quasi-extinction due to the dissipation of the disease at low [population] densities," the study found.
"Although epidemics in this species may not result in extinction directly, the contemporary presence of additional mortality sources during periods of low abundance may increase extinction risk."
Department of Primary Industries, Water and Environment biologist Claire Hawkins said Tasmanian researchers thought DFTD was probably density dependent but the necessary data had not yet been collected.
"If it's an infectious disease, we are expecting at some low-density level the disease is likely to fizzle out," Dr Hawkins said.
"We are focusing much more on the behaviour of the disease now and how the disease is changing the populations."
University of Tasmania researcher Menna Jones said it could be two or three years before enough data was collected to verify speculation about the impact of DFTD.
"You need to get the sample size up high enough to get enough data to be sure about the patterns you are seeing," Dr Jones said.
Statistical modelling by the Charles Darwin University researchers found major population cycles in the devil population occurred every 77 to 146 years. These cycles appear consistent with anecdotal but as yet unconfirmed reports that the devil had experienced previous boom-and-bust population cycles.
Tasmanian devil expert Eric Guiler has long thought the devil population has suffered at least three population crashes since British colonisation. Dr Guiler's evidence, however, was only anecdotal as little devil population research was done prior to the 1960s. It has been suggested that a bust cycle is thought to have led to a genetic bottleneck, which has made the contemporary devil population very closely related.
The research from Charles Darwin University suggests major population cycles could occur and be "consistent with historical reports".
