Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Ancient diets of Australian birds point to big ecosystem changes

08.07.2005


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. Photo by G H Miller


7 Plant ecosystems in monsoonal Australia burn frequently through natural ignition by lightning strikes during the build up to the wet season, when dry lightning storms are common. But burning is also promoted by human ignition, from both traditional burning practices of Aboriginal Australians and governmental land managers. In Kakadu, a World Heritage Area east of Darwin, ecosystems have adapted to millennia of Aboriginal burning. Consequently, land managers strive to maintain the "natural" vegetation through prescribed burns in consultation with Aboriginal advisors. Land managers deliberately set this fire, 100 km south of Darwin. Photograph by Gifford H. Miller, Sept. 1998.



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."

Gifford Miller | EurekAlert!
Further information:
http://www.colorado.edu

More articles from Ecology, The Environment and Conservation:

nachricht Dispersal of Fish Eggs by Water Birds – Just a Myth?
19.02.2018 | Universität Basel

nachricht Removing fossil fuel subsidies will not reduce CO2 emissions as much as hoped
08.02.2018 | International Institute for Applied Systems Analysis (IIASA)

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

Im Focus: Like a wedge in a hinge

Researchers lay groundwork to tailor drugs for new targets in cancer therapy

In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Magnetic nano-imaging on a table top

20.04.2018 | Physics and Astronomy

Start of work for the world's largest electric truck

20.04.2018 | Interdisciplinary Research

Atoms may hum a tune from grand cosmic symphony

20.04.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>