Humans, climate change 'killed Ice Age mammals'

For decades, scientists have been debating the reasons behind the enigmatic mass extinctions of the Late Quaternary period, which caused the loss of a third of the large mammal species in Eurasia, two thirds of species in North America and 90 per cent of the large mammal and bird species in Australia.

In particular, the roles played by climate and humans in driving the extinction of the large mammals, called megafauna, have remained contentious.

Now, an international team,     involving over 40 academic institutions around the world, studied the extinction of six Ice Age mammals and found the impacts of climate change and humans had dramatically different consequences for each of the species, the 'Nature' journal reported.

"We found that the large mammals who went extinct in the Ice Age were strongly influenced by changes in climate and habitat, which raises concerns about the impact of future climate change on modern large animal species," said Dr Simon Ho at the University of Sydney, a team member.

To disentangle the processes underlying megafaunal extinction, researchers combined information from ancient DNA, climate data, and the archaeological record to examine the extinction of six herbivorous mammals -- woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox.

The results showed that neither climate nor human occupation alone can explain the megafaunal extinctions of the late Quaternary, but rather that each species has responded differently to the effects of climate change, habitat shifts and human encroachment.Dr Ho said: "The results are more complicated that we previously thought. Our study indicates that humans played no part in the extinction of the woolly rhinoceros or the musk ox in Eurasia and that their demise can be entirely explained by climate change.

"On the other hand, humans aren't off the hook when it comes to the extinction of the wild horse and the bison in Siberia. Along with climate change, our ancestors share responsibility for these megafaunal extinctions.

"Although the reindeer was relatively unaffected by either of these factors, the causes of the extinction of the woolly mammoth remains a mystery."

According to lead researcher, Eske Willerslev at the University of Copenhagen, the latest findings put an end to the single-cause theories of the Ice Age extinctions.

"The study suggests that care should be taken in making generalisations not just regarding past and present species extinctions but also those of the future; the impacts of climate change and human encroachment on species extinctions depends on which species we're looking at," Willerslev added.

Despite the unparalleled amount of data analysed in this study, the team found no clear pattern distinguishing species that went extinct -- such as the woolly rhinoceros and woolly mammoth -- from those that survived -- such as the wild horse in Eurasia and reindeer in North America -- suggesting that it will be challenging for experts to predict how modern mammals will respond to future global climate change.