Posted on 2 November 2011
In one of the biggest studies of its kind, an inter-disciplinary team from more than 40 universities around the world, led by the University of Copenhagen and including scientists from the University of York, tried to answer the contentious question: was it climate change or human interference that caused the extinction of large-bodied mammals (“megafauna”) such as the Eurasian musk ox and steppe bison?
Their findings, published online today in the journal Nature, show dramatically different reactions for different species, making it harder for experts to know how existing mammals will respond to future changes in the Earth’s temperatures.
Scientists have tried for decades to disentangle the roles of climate change and human interference in species loss. Past research indicates both factors played a part, with extinctions greatest on continents with the most dramatic climate changes, and species loss in North America and Australia coinciding with the arrival of humans.
During the Late Quaternary period, Europe and Asia lost about 36% of their large-bodied mammals, while North America lost 72%.
Researchers examined more than 10,000 specimens made up of ancient DNA sequences, megafauna and human remains to discover how woolly mammoth, woolly rhinoceros, wild horse, reindeer, bison and musk ox behaved during the Late Quaternary period (the past 50,000 years), a time of enormous environmental stress when the Earth moved from an Ice Age to its current warm spell.
They found that while climate change appeared to have caused the extinction of Eurasian musk ox and woolly rhinoceros, a combination of climate and human impact drove the demise of wild horse and steppe bison.
But they were left puzzled by the behaviour of the woolly mammoth, whose population grew five to tenfold between 34,000-19,000 years ago (at least 10,000 years after first human contact) before slowly dying out.
It is remarkable that despite the huge amount of data analysed in this study no clear pattern emerged... each species reacts differently to environmental changes
Professor Michi Hofreiter
Reindeer remained relatively unaffected on a global scale by humans and climate, possibly due to their high reproductive capacity and ecological flexibility.
The researchers showed that changes in habitat distribution and population size are intrinsically linked over evolutionary time, supporting the view that populations of many species will decline in the future owing to climate change and habitat loss. But they found no distinguishing characteristics in the rate or pattern of decline in those species that went extinct compared with those that survived.
Professor Michi Hofreiter, of the Department of Biology at York and a member of the York Centre for Human Palaeo-ecology and Evolutionary Origins (PALAEO), said: “It is remarkable that despite the huge amount of data analysed in this study no clear pattern emerged that allows distinguishing surviving from extinct species. This shows that each species reacts differently to environmental changes. Therefore, we should probably be very careful with making generalizations, both about what happened in the past and what might happen in the future.”
The study involved biologists, palaeontologists, climate modellers, as well as experts in extinction, palaeo-environmental reconstruction and biological tolerances.