Did dingo attacks drive the Tassie tiger extinct?

By Patrick Hsiao 4 May 2012
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A size estimate of mainland thylacines shows they were smaller and more vulnerable than their Tasmanian cousins.

ATTACKS BY DINGOES may have been a major factor that drove the Tasmanian tiger, or thylacine, extinct on the Australian mainland 3500 years ago, says a new study.

Up until now, experts had thought that an improvement in human technologies for hunting or competition with dingoes for prey were some of the most likely causes of the decline. Thylacines were thought to have been significantly larger than dingoes, and therefore would have had little to fear from them.

However, a new analysis of fossil bones led by Dr Michael Letnic, an ecologist at the University of Sydney, suggests that thylacines on the mainland may have been equal in size or smaller than dingoes, making them vulnerable to predation from them.

Revising the role of the dingo

“This study changes our understanding about the role of the dingo and presents a good argument and case they were large enough to kill a thylacine,” Michael told Australian Geographic.

The thylacine was Australia’s largest surviving marsupial predator until the last known individual died in Hobart Zoo in 1936. Both thylacines and Tasmanian devils disappeared on mainland Australia sometime after the dingo was introduced, possibly by seafarers from China. They continued to keep a toehold on Tasmania which remained dingo-free.

Michael says his team were aware of historic reports that mainland thylacines were smaller than Tasmanian ones, so they wanted to explore the idea.

“Modern ecological studies show that larger predators frequently kill smaller predators, so we decided to test the hunch that dingoes were actually larger than thylacines and caused their extinction by killing them in direct confrontations,” he says.

Females thylacines fox sized

By measuring head size and the thickness of limb bones in semi-fossilised thylacine remains from Western Australia, the researchers were able to make the first accurate size comparisons with dingoes. The results revealed that mainland male thylacines would likely have matched dingoes for size, but females would have been significantly smaller.

“Dingoes were almost twice as large as female thylacines, which were not much bigger than a fox,” says Michael. “These results support the hypothesis that dingoes would have been dominant in one-on-one [confrontations]…owing to their larger body size.”

Particularly, attacks from dingoes on the smaller and more vulnerable female thylacines may have impacted breeding rates, he says.

“The study gives clear evidence for the influence of dingoes on the mainland population, whether through direct killing or simply by out-competing them for smaller prey animals,” comments Dr Brandon Menzies, a University of Melbourne zoologist who was not involved in the study.

Tasmanian tigers had low diversity

Brandon’s own study, published in April, shows that Tasmanian thylacines suffered from low genetic diversity – possibly a result of isolation on an island. This may have contributed to their extinction. Tasmanian devils have very low diversity today, which is why an infectious facial cancer has been able to spread across the population.

Additionatlly, Michael says the skull measurments he’s made have revealed that thylacines had much smaller brains than dingoes “so they may have outwitted them, too,” possibly giving dingoes an edge in both confrontations and competition for prey. 

The study is published this week in the journal PloS One.