June 5, 2014
Humans, Not Climate Change, Led To Extinction Of Mammal Giants
Alan McStravick for www.redorbit.com - Your Universe online
We could be living in a world populated with giant deer, wombats, sabre-toothed cats, marsupial lions and kangaroos but for one important factor: humans killed them all. A new study out of Aarhus University, Denmark's second oldest university, looked back over the past 100,000 years and determined that human expansion and competition, not climate change, marched these and many other large mammals right out of the Animal Kingdom. This study marks the first time a complete global analysis of large mammal extinction has been carried out.
Over the last half century, there has been a growing discussion about the mass extinction event that occurred during and immediately after the last Ice Age. From this discussion two viable theories had arisen as possible explanations for just what exactly happened to many of the mammals that we now only know about thanks to their presence in the fossil record.
The first of the two theories centered on the idea that climate change that resulted in the last Ice Age was primarily responsible for stressing the multiple species to such an extent that they ultimately perished from the face of the Earth. The argument contends that these animals struggled to seek out suitable habitats and thus died out as a result. An issue with this theory, however, is that the Ice Age of 100,000 years ago was not the first Ice Age this planet has been made to endure and previous examples of extreme cooling failed to produce a corresponding extinction rate anywhere near what occurred in our most recent extreme climate change.
The other popular theory is that of overkill. The idea stems from the diaspora of modern man out of Africa to all points, far and wide. As man entered new ecosystems and habitats, large mammals were either exterminated outright or faded away due to their direct competition with man for common prey. Early modern man clearly thrived due to his apex predator abilities of hunting and gathering.
The Aarhus University study researchers produced the first global analysis and relatively fine-grained mapping of all the large mammals that existed between 132,000 and 1,000 years ago. This span of time is representative of the period during which the extinction event took place. Large mammals were defined as having a weight of at least 22 lbs. By focusing on the multiple global regions, the team was able to study the geographical variation in the percentage of extinctions of large species on a level far more magnified than ever done previously.
Over the 131,000-year span of time, the researchers determined a total loss of large mammal species of 177. While this figure may, for the amount of time reviewed, seem negligible it is important to point out that 177 extinct species is considered a massive loss, ecologically speaking. Breaking this figure down by continent, the team showed a loss of 18 and 19 species in Africa and Europe, respectively; Asia lost 38 species; and in Australia and the surrounding areas, a total of 26 species became extinct. But one only need to travel to North and South America to find the biggest losses. It was in North America that 43 species ceased forever to exist while South America puts up the staggering figure of 62 total large mammal species erased from existence.
Regardless of the actual climes experienced during the last Ice Age, the extinction of large animals affected all regions and all species. For example, cold-adapted animals like the woolly mammoth fared as well as the forest elephants and giant deer of the temperate zones and the giant sloths and Cape buffalo that lived in more tropical zones. As noted above, species loss was experienced on virtually every continent.
The Aarhus University team placed their findings against the idea that climate was responsible for the massive die-off and found that correlation wanting. The only area that it appeared it may have played any role is the area in and around the Ural Mountains that separate Asia from Europe, also known as Eurasia.
“The significant loss of megafauna [large mammals] all over the world can therefore not be explained by climate change, even though it has definitely played a role as a driving force in changing the distribution of some species of animals,” explained Postdoctoral Fellow Christopher Sandom. He continued, “Reindeer and polar foxes were found in Central Europe during the Ice Age, for example, but they withdrew northwards as the climate became warmer.”
The second prevailing theory of the last half-century showed far more promise for explaining the mass extinction of large mammals. A very strong correlation between the extinction and the history of human expansion definitely exists.
“We consistently find very large rates of extinction in areas where there had been no contact between wildlife and primitive human races, and which were suddenly confronted by fully developed modern humans (Homo sapiens). In general, at least 30 percent of the large species of animals disappeared from all such areas,” says Professor Jens-Christian Svenning.
In addition to pointing the finger squarely at humans and their massive and rapid global expansion, the study results also highlight the similarities apparent in the prehistoric extinction of large animals due to hunting (eg. The American and European bison, quagga, Eurasian wild horse or tarpan) and our modern day flirtation with extinction thanks to modern hunting and poaching behaviors (eg. The rhino poaching epidemic)
The Aarhus University team has published the results of their study in an article entitled "Global late Quaternary megafauna extinctions linked to humans, not climate change" in the journal Proceedings of the Royal Society B.