News in Science

Ice age animals not wiped out by humans

Ancient animals The extinction of the woolly mammoth and other large ice age animals can't be blamed on a 'human blitzkrieg', say researchers.

A new study shows the apparent mass extinction was due instead to a combination of climate change, habitat loss as well as human impact.

The findings have been hailed as a "fantastic development in the debate on extinction" and a key to developing strategies to prevent further loss of species.

The research, published today online in Nature, tracks the extinction of six large mammals during the last ice age and shows while climate is the major driver of population change, each species reacted differently to the effects of climatic shifts.

Towards the end of the Late Quaternary, beginning around 50,000 years ago, Eurasia and North America lost about 36 per cent and 72 per cent of its megafauna, respectively.

Debate over the cause of these extinctions has focused on the primacy of humans and climate in driving this dramatic loss of large mammals.

An international team, led by Professor Eske Willerslev of the Centre for GeoGenetics at the University of Copenhagen, from 43 institutions analysed the extinction of a number of herbivorous mammals at the time.

Using a combination of climate data, ancient DNA, species distribution models and the human fossil record to show human overlap with the animals, the researchers show the extinction of these megafauna cannot be attributed either solely to climate change, or to overhunting.

Instead, the study shows many factors unique to each species are responsible for their disappearance including a loss of genetic diversity, isolation by distance of animal populations, and in some cases a drop in population numbers.

Mammoth evidence

Interestingly the study shows the woolly rhinoceros (Coelodonta antiquitatis) and Eurasian woolly mammoth (Mammuthus primigenius) experienced a five- to tenfold increase in effective population size at least 10,000 years after first human contact.

This result directly contradicts models of population collapse from human overkill (blitzkrieg) or infectious diseases following the first human contact (hyperdisease).

Based on a lack of overlap between the animal and human populations, the researchers find climate change alone explains the extinction of the musk ox (Ovibos moschatus) and woolly rhinoceros.

Specimens of the musk ox were found in only 1 per cent of European archaeological sites while woolly rhinoceros remains were in just 11 per cent of Siberian archaeological sites, suggesting it was not a common prey species for humans.

A combination of climatic and human influences seem to be responsible for the loss of wild horses (Equus ferus) and ancient bison (Bison priscus/Bison bison), whose remains are most commonly found in archaeological sites.

Reindeer unaffected

By contrast, reindeer (Rangifer tarandus) remained relatively unaffected and are found in the millions in the northern arctic regions today. The researchers suggest this animal survived because of high levels of fecundity and ecological flexibility and continuing low levels of isolation by distance.

The causes underlying the extinction of woolly mammoth remain elusive however, the authors say. While there is great overlap between humans and the ancient elephant, the researchers find a marked drop in woolly mammoth remains in Siberian archaeological sites after the ice age peaks around 19,000 years ago (43 per cent of sites to 30 per cent of sites).

The researchers say this could be due to a northward range shift in the mammal, a scarcity of the beast, or an increasing human preference for other prey species.

Large scale study

Co-author Dr Simon Ho, of the School of Biological Sciences at the University of Sydney, says the strength of the study lies in its unprecedented scale.

Ho says about 1000 ancient DNA sequences, 3000 dated megafauna specimens and 6000 radiocarbon dated remains from the human fossil record were analysed for the study.

He says where theories of extinction have previously fallen into two camps — either climate- or human-caused, their study shows a more complicated picture.

"The way species reacted to changes in climate and habitat is so different," he says.

"The extinctions differ from species to species, and we don't find any common genetic characteristic to distinguish extinct from surviving species."

Research Fellow in Archaeology, Dr Judith Field, at the University of Sydney, has long argued against the human blitzkrieg theory of extinction.

She says the study is a "fantastic development".

"It is a long time coming and marks a turning of the tide in how we approach these extinctions of the Late Quaternary," she says.

"All the species follow different extinction patterns. It brings climate change and the implications of habitat fragmentation to the fore again."

Staggered extinctions

Field says the data shows a pattern of staggered extinctions.

"None of it lines up to say a mass extinction and there is very little evidence to say humans drove the extinction. It shows it is an ecological problem where humans are a factor," says Field.

However she does not believe the paper will settle the debate between Australian scientists as she says the "human blitzkrieg" school are "so wedded to their positions."

Ho says it would be impossible to replicate the study for Australian megafauna because of a lack of specimens.

"The problem in Australia is the hot climate means ancient specimens aren't preserved," he says.

Field agrees but says the data that is available follows the staggered pattern seen in Eurasia and North America and would indicate a similar combination of factors drove the extinction of Australian megafauna.

"If it is happening in Eurasia and happening in North America, similar processes must be happening elsewhere," she says.

Field says the study is the "strongest, most detailed and well presented" to date and will provide a great base on which to produce predictive studies and develop strategies to see what species will be threatened in the future.