Featured Research

from universities, journals, and other organizations

Ancient Diets Of Australian Birds Point To Big Ecosystem Changes

Date:
July 10, 2005
Source:
University of Colorado at Boulder
Summary:
A shifting diet of two flightless birds inhabiting Australia tens of thousands of years ago is the best evidence yet that early humans may have altered the continent's interior with fire, changing it from a mosaic of trees, shrubs and grasses to the desert scrub evident today, according to a University of Colorado at Boulder-led team.

Nearly intact eggshell of the extinct giant bird Genyornis newtoni, discovered near Port Augusta, South Australia in 2002. Note puncture hole from predator in upper left. The egg has been dated by both Optically Stimulated Luminescence (OSL) and Amino Acid Racemization (AAR) at 60,000 years, about 10,000 years before megafaunal extinction.
Credit: Photo by G. H. Miller

A shifting diet of two flightless birds inhabiting Australia tens of thousands of years ago is the best evidence yet that early humans may have altered the continent's interior with fire, changing it from a mosaic of trees, shrubs and grasses to the desert scrub evident today, according to a University of Colorado at Boulder-led team.

The unprecedented ecosystem disruption is now thought to have led to the extinction of Australia's large terrestrial mammals, which disappeared shortly after humans colonized the continent about 50,000 years ago, said Professor Gifford Miller of CU-Boulder's Institute of Arctic and Alpine Research. Scientists have shown there were no significant swings in the continent's climate during that period, leading most to believe that humans had a hand in the extinctions through over-hunting, spreading disease or by altering the vegetation of the vast interior through systematic burning.

Using isotopic studies of fossil eggshells from both indigenous emus and the extinct, ostrich-sized Genyornis, a new study by Miller and colleagues publishing in the July 8 issue of Science magazine shows that the ecosystem's flora changed swiftly and dramatically after humans arrived.

The analyses, which scientists used to pinpoint particular plant groups ingested by the birds, indicated that emus living before 50,000 years ago preferred nutritious grasses characteristic of milder temperatures and warm summer rains, Miller said. After 45,000 years ago, the eggshell evidence showed emus successfully switched to a diet of mostly shrubs and trees characteristic of drier conditions, he said.

But according to the research team, Genyornis -- which also preferred the nutritious grass prior to 50,000 years ago -- failed to make the dietary switch and became extinct shortly after humans arrived, he said.

"The opportunistic feeders adapted and the picky eaters went extinct," said Miller. "The most parsimonious explanation is these birds were responding to an unprecedented change in the vegetation over the continent during that time period."

Other study authors included Marilyn Fogel of the Carnegie Institution in Washington, D.C., John Magee and Michael Gagan of Australian National University in Canberra, Simon Clarke of Australia's Wollongong University and Beverly Johnson of Bates College in Lewiston, Maine.

The researchers analyzed nearly 1,500 fragments of fossilized emu and Genyornis eggshells dating back 140,000 years from three different regions in Australia's interior, including Lake Eyre, Port Augusta and the Darling-Murray Lakes. Each region has a distinct local climate and geography, he said.

They also looked at carbon isotopes in fossil wombat teeth collected from the Port Augusta and Darling-Murray sites, where such teeth often are found in association with fossil-bird eggshells. While the analyses showed the diet of the vegetarian wombat consisted of a much larger proportion of the grasses favored by emus and Genyornis prior to 50,000 years ago, wombats, like emus, successfully switched to other vegetarian food sources after 45,000 years ago.


"Neither over-hunting nor human-induced diseases, the two most widely cited alternative agents for a human-caused extinction event in Australia, would result in the dramatic changes at the base of the food web documented by our datasets," wrote the authors in Science. "The reduction of plant diversity, however it came about, would have led to the extinction of specialized herbivores and indirectly to the extinction of their non-human predators."

In January 2005, Miller and colleagues published a paper in Geology suggesting burning by ancient hunters and gatherers triggered the failure of the annual Australian monsoon over the interior thousands of years ago by altering the flora enough to decrease the exchange of water vapor between the biosphere and atmosphere.

Lake Eyre, a deep-water lake in Australia's interior that was filled by regular monsoon rains about 60,000 years ago, is now a huge salt flat that only occasionally is covered by a thin layer of salty water.

The earliest human colonizers in Australia are believed to have arrived by sea from Indonesia about 50,000 years ago, using fire as a tool to hunt, clear paths, signal each other and promote the growth of certain plants, Miller said.

More than 85 percent of Australia's large mammals, birds and reptiles weighing more than 100 pounds went extinct shortly after humans arrived, including 19 species of marsupials, a 25-foot-long lizard and a Volkswagen-sized tortoise, he said.

"This study shows that the environmental footprints of humans can have very large and unexpected consequences, which I think is relevant to what is happening with human activity on Earth today," said Miller. "A cumulative series of small changes can have unintended large-scale, consequences, in this case a complete restructuring of the ecosystems."

###

The U.S. National Science Foundation and the Australian Research Council funded the study with additional support from Australian National University and CU-Boulder.



Story Source:

The above story is based on materials provided by University of Colorado at Boulder. Note: Materials may be edited for content and length.


Cite This Page:

University of Colorado at Boulder. "Ancient Diets Of Australian Birds Point To Big Ecosystem Changes." ScienceDaily. ScienceDaily, 10 July 2005. <www.sciencedaily.com/releases/2005/07/050709001735.htm>.
University of Colorado at Boulder. (2005, July 10). Ancient Diets Of Australian Birds Point To Big Ecosystem Changes. ScienceDaily. Retrieved October 1, 2014 from www.sciencedaily.com/releases/2005/07/050709001735.htm
University of Colorado at Boulder. "Ancient Diets Of Australian Birds Point To Big Ecosystem Changes." ScienceDaily. www.sciencedaily.com/releases/2005/07/050709001735.htm (accessed October 1, 2014).

Share This



More Fossils & Ruins News

Wednesday, October 1, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

2,000 Year Old Pre-Inca Cloak on Display in Lima

2,000 Year Old Pre-Inca Cloak on Display in Lima

AFP (Sep. 27, 2014) A 2,000 year-old Pre-Inca cloak that is believed to represent an agricultural calendar of the Paracas culture is on display in Lima. Duration: 00:39 Video provided by AFP
Powered by NewsLook.com
Original Mozart Sonata Manuscript Found in Budapest

Original Mozart Sonata Manuscript Found in Budapest

AFP (Sep. 26, 2014) Considered lost for over two centuries, the original manuscript of one of the most famous works of Mozart's Sonata in A major has been uncovered in a library in Budapest. Duration: 01:04 Video provided by AFP
Powered by NewsLook.com
Underground Art Reveals WW1 Soldiers' Hopes and Fears

Underground Art Reveals WW1 Soldiers' Hopes and Fears

AFP (Sep. 25, 2014) American doctor and photographer Jeff Gusky reveals the underground quarries used by the soldiers of World War One, and the artwork they left behind which illustrates their hopes and fears. Duration: 02:15 Video provided by AFP
Powered by NewsLook.com
Raw: Ice Age Wooly Mammoth Remains for Sale

Raw: Ice Age Wooly Mammoth Remains for Sale

AP (Sep. 23, 2014) A rare, well-preserved skeleton of a woolly mammoth is going on sale at Summers Place Auctions hope the 11.5-foot tall, almost intact specimen will fetch between $245,000 to $409,000. (Sept. 23) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins