February 1, 2013
Humans, Not Disease, Drove Tasmanian Tiger To Extinction
April Flowers for redOrbit.com - Your Universe Online
A new study led by researchers at the University of Adelaide concludes that humans alone may have been responsible for the extinction of Australia's iconic native predator, the Tasmanian Tiger (thylacine). The study, published in a recent issue of the Journal of Animal Ecology, used a new population modeling approach to contradict the widespread belief that disease must have been a factor in the thylacine's extinction.The Tasmanian Tiger (Thylacinus cynocephalus) looked like a long-bodied dog with stripes, a stiff, heavy tail and large head. Adults measured about six feet long from nose to the tip of the tail, stood about 2 feet high at the shoulder and weighed around 65 pounds. A meat eater, the Tasmanian Tiger was the world's largest marsupial after the Thylacoleo, Australia´s marsupial lion that went extinct some 2 million years ago. For the most part, their diet consisted of wallabies, along with various small animals and birds.
The Tasmanian Tiger was found throughout most of Tasmania before European settlement in 1803. They were driven to near extinction between 1886 and 1909 largely thanks the Tasmanian government which encouraged people to hunt them. The government paid bounties for over 2000 carcasses during this time. The last known thylacine was captured from the wild in 1933. That specimen died at the Hobart Zoo in 1936, according to the Tasmanian Department of Primary Industries, Parks, Water and Environment (DPIW).
There have been hundreds of sightings since 1937, but no conclusive evidence that the thylacine still lives in the wild. A study of the sighting reports between 1934 and 1980 concluded that just under half of them (320) could be considered good and credible. However, many extensive physical searches have turned up no evidence so far, and the species was officially declared extinct in 1986.
"Many people, however, believe that bounty hunting alone could not have driven the thylacine extinct and therefore claim that an unknown disease epidemic must have been responsible," says the project leader Dr. Thomas Prowse of the University of Adelaide´s School of Earth and Environmental Sciences and the Environment Institute.
Scientists and popular theory have long held that the thylacine died of a distemper-like disease. A 2012 study also indicated that the extinction of the carnivorous marsupials have also been due in part to a lack of genetic diversity among their small populations.
"We tested this claim by developing a 'metamodel' — a network of linked species models — that evaluated whether the combined impacts of Europeans could have exterminated the thylacine, without any disease."
The team of conservation scientists used a mathematical model called a population viability analysis (PVA) to simulate different management strategies. Traditionally, these PVA models neglect important interactions between species. However, the researchers on this study designed a new approach to PVA that included species interactions.
"The new model simulated the direct effects of bounty hunting and habitat loss and, importantly, also considered the indirect effects of a reduction in the thylacine's prey (kangaroos and wallabies) due to human harvesting and competition from millions of introduced sheep," says Prowse.
"We found we could simulate the thylacine extinction, including the observed rapid population crash after 1905, without the need to invoke a mystery disease. We showed that the negative impacts of European settlement were powerful enough that, even without any disease epidemic, the species couldn't escape extinction."
Fossil evidence and Aboriginal rock paintings show that the thylacine once roamed Australia, New Guinea and Tasmania. Scientists also suspect that predation and competition from Australia´s native wild dog, the dingo, may have accelerated its disappearance outside of Tasmania.