Ancient mammal species felt the human blow, study suggests
An international team of scientists led by the University of Copenhagen in Denmark suggests that anthropogenic activity and climate change played havoc on the genetic history of 6 large herbivores, potentially triggering the extinction or near extinction of large mammal populations within the last 10,000 years. The findings, published in the journal Nature, help piece together the puzzle on the possible fates of living mammal species as Earth continues to deal with global warming.
'Our findings put a final end to the single-cause theories of these extinctions,' explains senior author Professor Eske Willerslev of the Centre for GeoGenetics at the University of Copenhagen. 'Our data suggest care should be taken in making generalisations regarding past and present species extinctions; the relative impacts of climate change and human encroachment on species extinctions really depends on which species we're looking at.'
Co-author Beth Shapiro, the Shaffer Associate Professor of Biology at Pennsylvania (Penn) State University in the United States points out that the 6 species - the woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox - were at their prime during the Pleistocene Epoch (a period that lasted from around 2 million to 12,000 years ago).
'During this time, there were lots of climatic ups and downs - oscillations between long, warm intervals called interglacial periods, during which the climate was similar to what we have today, followed by long, cold intervals called glacial periods, or ice ages,' Professor Shapiro explains. 'Although these cold-adapted animals certainly fared better during the colder, glacial periods, they still managed to find places where the climate was just right - refugia - so that they could survive during the warmer, interglacial periods. Then, after the peak of the last ice age around 20,000 years ago, their luck started to run out. The question is, what changed? Why were these mammals no longer able to find safe refugia where they could survive in a warm climate?'
In order to the get to the bottom of things, the researchers compiled various data to test theories about how, when and why the woolly rhinoceros, woolly mammoth and wild horse became extinct after the last ice age, and why the reindeer, bison and musk ox survived.
'One source of information we used was DNA from the animals themselves,' the Penn State researcher explains. 'With genetic data, it's possible to estimate when and how much populations were able to grow and shrink as the climate changed and their habitat started to disappear.'
Climatic data from the glacial and interglacial periods, particularly temperature and precipitation patterns, were gathered as well. The team also collected archaeological data in order to evaluate the extent to which our early ancestors could have impacted the survival of the six species.
'For example, in locations where animal bones had been cooked or converted into spears, we know that humans lived there and were using them as a resource,' Professor Shapiro reveals. 'Even where we don't find evidence that humans were using the animals, if humans and the animals lived in the same place and at the same time, humans could have had some influence on whether the animals survived or not.'
The team discovered that save for the woolly rhinoceros, whose range never overlapped with that of humans, the other five mammal species were impacted by human activity, particularly since our ancestors kept the animals from finding alternative refugia especially because the human species began growing significantly.
'The take-home message is that during the most recent warming event, when the last ice age faded into the warm interval we have today, something kept these animals from doing what they had always done, from finding alternative refugia - less-than-ideal, but good-enough chunks of land on which to keep their populations at a critical mass,' Professor Shapiro says. 'That 'something' was probably us - humans.'
The findings indicate that while warm periods forced these species to face challenges, it was evolutionary events that had a bigger affect on them.
'We couldn't pinpoint what patterns characterise extinct species, despite the large and varying amount of data analysed,' comments lead author Eline Lorenzen of the University of Copenhagen. 'This suggests that it will be challenging for experts to predict how existing mammals will respond to future global climate change - to predict which species will go extinct and which will survive.'
The team of experts were palaeontologists, geologists, geneticists and climate modellers from Argentina, Australia, Canada, China, Denmark, Germany, the Netherlands, Norway, Panama, Russia, Spain, Sweden, the United Kingdom and the United States.
Data Source Provider: Nature; University of Copenhagen; Penn State
Document Reference: Lorenzen, E.D., et al. (2011) 'Species-specific responses of Late Quaternary megafauna to climate and humans', Nature, published 2 November. DOI: 10.1038/nature10574.
Subject Index: Biotechnology; Climate change & Carbon cycle research; Coordination, Cooperation; Scientific Research; Social Aspects