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Hunters, destruction of habitat, climate-change.


Press Release


     UC Berkeley Press Release

Climate change plus human pressure caused large mammal extinctions in 
late Pleistocene

By Robert Sanders, Media Relations | 30 September 2004

BERKELEY - A University of California, Berkeley, paleobiologist and his 
colleagues warn that the future of the Earth's mammals could be as dire 
as it was between 50,000 and 10,000 years ago, when a combination of 
climate change and human pressure resulted in the extinction of 
two-thirds of all large mammals on the planet.

Paleobiologist Anthony D. Barnosky and his colleagues reached this 
conclusion after review of studies of the extensive large mammal, or 
megafauna, extinctions that occurred in the late Pleistocene, when 
animals such as mammoths and mastodons, the saber-toothed cat, ground 
sloths and native American horses and camels went extinct.

jumble of fossil mammoth bones
A jumble of fossil mammoth bones being excavated from a fossil site in 
southeastern Washington state. Mammoths, which looked like shaggy 
elephants, were hunted by prehistoric humans who arrived in North 
America about 11.4 thousand years ago, as shown by the close 
intermingling of spearpoints with fossil mammal skeletons. However, they 
also went extinct coincident with climate change in areas where 
significant human presence has not been shown, such as Alaska, and 
coincident with climate change in areas where they had coexisted with 
humans for hundreds of thousands of years, such as parts of Europe. 
(Anthony D. Barnosky photo)

In the forensic quest for who done it, many have pointed fingers 
squarely at humans.

But in a review appearing in the Oct. 1 issue of /Science/, Barnosky and 
his colleagues conclude that climate change also played a big role in 
driving these extinctions.

Barnosky's colleagues in the study are Paul Koch, professor of earth 
sciences at UC Santa Cruz; Scott Wing, a paleobotanist in the Department 
of Paleobiology at the Smithsonian Institution's National Museum of 
Natural History; UC Berkeley graduate student Alan Shabel; and recent UC 
Berkeley Ph.D. Bob Feranec, now a post-doctoral fellow at Stanford 
University.

"There's been a lot of talk about people causing the extinction of the 
megafauna by killing everything they saw, like a blitzkrieg," said 
Barnosky, professor of integrative biology and a curator in UC 
Berkeley's Museum of Paleontology. "But if you look at all the evidence, 
it's clear that while humans had a major role in these extinctions, in 
many cases climate change was a key part of the recipe.

"Humans and climate change were the one-two punch that drove extinction 
between 50,000 and 10,000 years ago, and the same thing is happening in 
a major way today."

Because climate change is occurring more rapidly today than even in the 
late Pleistocene, when the majority of megafauna went extinct, serious 
consequences for many large animal species that weathered the 
Pleistocene extinction could be just down the road, Barnosky said. And 
the impact could be even greater today because of impoverished large 
animal populations and surging populations of humans taking over former 
large-animal habitats.

"Human activities today, combined with climate change, probably are 
going to result in inevitable extinction of many more species and 
unpredictable ecosystem changes," he said.

The authors' warnings are based on a review of previous studies of 
Pleistocene animal extinctions around the world, from Australia to 
Europe to North America. The Pleistocene, a period starting about 1.8 
million years ago, was a time of glacial comings and goings, with more 
than 20 cycles of cooling and warming that concluded only about 10,000 
years ago with the end of the last ice age.

In previous studies of animal remains layered in caves in the American 
West, Barnosky has found that during some of the last few 
glacial/interglacial cycles between 1 million and 600,000 years ago, the 
number of small, medium and large mammals in a given community remained 
fairly stable, though different species may have filled the various 
ecosystem niches. In the late Pleistocene, however, something happened 
to make the number of large mammals nosedive continent-wide.

This new analysis of archeological, climatic, ecological and simulation 
studies shows that these extinctions happened around the world. Of more 
than 150 genera of megafauna - that is, animals weighing more than 44 
kilograms (97 pounds) - living on Earth 50,000 years ago, at least 97 
were extinct by 10,000 years ago. If you look at localized extinctions 
instead of global extinctions, 121 genera disappeared from at least one 
continent.

Those blaming humans ascribe the extinctions to human hunting, either 
through overkill - hunting that could have led to extinction in about 
1,500 years - or through a "blitzkrieg" of hunting that could have 
knocked off a species in less than 500 years. Another suggestion, dubbed 
"sitzkrieg" after the term for a "sitting" war that shows slow or no 
progress, is that humans caused extinction through long-term habitat 
alteration.

Barnosky and his colleagues found sparse evidence outside Australia that 
humans were the sole cause of extinction. Data are sketchy for the 
Australian continent, Barnosky cautioned, but little climate change was 
going on at the time of extinction between 40,000 and 50,000 years ago. 
However, humans were certainly on the scene, and some scientists think 
that fires set by humans had as much to do with extinction as direct 
hunting. Over a few thousand years, Barnosky said, an extended sitzkrieg 
may have led to the extinction of large mammals such as kangaroos, 
wombats, the marsupial lion (/Thylacoleo carnifex/) and the largest ever 
marsupial, the 2 1/2-ton Diprotodon.

Elsewhere, human activities combined to a greater or lesser degree with 
climate change to lead to extinctions. In Europe and parts of Asia, 
mammals such as the giant Irish deer or Irish elk died out broadly 
toward the end of the late Pliestocene, in some areas before humans were 
present. Earlier, though, warm-adapted megafauna such as straight-tusked 
elephants (Palaeoloxodon) and hippos, which were abundant during 
preceding interglacials, disappeared with the cooling of the last ice 
age, starting around 45,000 years ago and persisting up to the height of 
the glacial period 20,000 years ago.

"This is a very clear case of climate-caused extinction without the 
significant input of humans," Barnosky said.

Similarly, in Alaska and the Yukon, the disappearances of short-faced 
bears, such as the grizzly-like Arctodus simus, the largest land 
carnivore ever to inhabit North America; mammoths; and two horse species 
occurred before apparent signs of human contact.

A second pulse of climate-caused extinctions began in Europe and Asia 
about 12,000 years ago as cold-adapted animals - the wooly rhino and the 
mammoth - died out with warming temperatures. But it's possible, 
Barnosky said, that the rise of modern humans - /Homo sapiens sapiens/ - 
with their broad variety of tools and diverse diet, negatively impacted 
these animals to an extent not seen in Europe with earlier human 
species, such as /Homo erectus/ and Neanderthals.

North America, in particular, is an example of a place where humans 
speeded the process of climate-caused extinction, in many cases by 
overkill. Evidence of mammoth kills date from near the first appearance 
of stone spearheads made by the human Clovis civilization 11,400 years 
ago. Only mammoths and mastodons have been found with incontrovertible 
evidence that they were killed by humans in North America, though human 
artifacts have been found in association with extinct megafauna fossils 
on all continents, including Africa.

Over a period of, at most, 1,500 years, following the appearance of 
Clovis-style hunters, camels and horses, rhinos and peccaries, 
short-faced bears and saber-toothed tigers, as well as the 
armadillo-like glyptodonts and the giant ground sloths (Megatheriadae), 
all disappeared from the North American continent.

"Humans and climate change came together at exactly the same time" to 
lead to these great megafauna extinctions, Barnosky said.

The case in South America is still muddled, he noted, but there, too, 
human incursions combined with climate change possibly coincided with 
the departure of large mammals, such as a variety of armadillos and 
llama- and camel-like animals, in a case similar to that in North 
America. In Africa, as well, it is unclear why any large mammals went 
extinct, since humans arose in concert with these animals and, by some 
arguments, they should have been in balance with one another. There, as 
in South America, the uncertainty comes from lack of data.

In these fairly recent large-mammal extinctions, Barnosky sees lessons 
for the future.

"Humans tend to impact the bigger animals, with the smaller animals as 
collateral damage," he said. "Climate change is just the opposite - it 
affects the little guy first and then, through them, the big guys. 
Today, we see humans taking out the bigger animals and climate change 
affecting the smaller animals, so we can expect to see some pretty 
dramatic changes in the ecosystem."

One major problem today is that, because of human encroachment, there 
are no refuges for animals that might want to relocate because of 
climate change.

"One thing we can do, as conservationists, is to create and connect 
natural areas" to allow animals to move around, he added. "Because 
species can no longer do this by themselves, maybe the solution is to do 
it for them."

The work was supported by the National Science Foundation.