This page is viewed 1746 times
Popular Archaeology It was the human hunter, not a changed climate, that led to the extinction of the giant Pleistocene herbivores of Australia and a transformed ecological landscape at least 40,000 years ago. 
According to the results of a recently completed study published in the March 23, 2012 issue of the journal Science, human hunters were largely responsible for the extinction of Pleistocene-age Australia's giant herbivores around 40,000 years ago. The extinction, as a result, led to significant changes in the ecological landscape, a cause-and-effect relationship that runs counter to the popular climate-centered theory for ecology shifts suggested by many other scientists. States Susan Rule of the Australian National University, Canberra and colleagues in their report: "Recent studies from North America [for example] show that megafaunal decline was followed by vegetation change and increased fire. However, these events happened in the latest Pleistocene during a time of rapid climate change, so it is difficult to resolve the contributions to them of megafaunal extinction versus climate."[1] Rule's research changes this. She and her colleagues collected and analyzed the pollen, charcoal and Sporormiella spore content of two sediment cores taken from a palaeolake/swamp in Lynch's Crater, a volcanic maar in Queensland, northeastern Australia. In antiquity, the crater was surrounded by tropical rainforest until European settlement. Sporormiella spores, key to the study, is a fungus that depends upon ingestion by herbivores to complete its life cycle. It is found in their dung, where it sporulates. What they found was that the Sporormiella spore counts dropped to nearly zero at 41,000 years ago, suggesting the absence or disappearance of herbivores in the environment of that time. The count change corresponded with subsequent changes in the pollen and charcoal content, signifying a change from a mixed rainforest environment to that of leathery-leaved, scrubby vegetation called sclerophyll along with an increase in fire activity. To complete the analysis, the researchers coupled their findings with climate data. "We compared the magnitude of the ecological changes that followed megafaunal decline around 41 ka with earlier climate-driven shifts from 74 and 120 ka," reports Rule, et. al. "There was no significant effect on Sporormiella from the two [previous] episodes of climate drying, suggesting that the megafaunal extinction was not the culmination of a long-term decline driven by an increasingly arid climate."[1] What does all of this mean? Rule and her colleagues suggest that the arrival of humans, not climate change, caused megafaunal extinction in this region of Australia. The changes measured in the study results coincide with the arrival of humans in the fossil record. This extinction, they conclude, in turn triggered the replacement of mixed rainforest by sclerophyll vegetation due to the resulting relaxed herbivore plant consumption pressure, causing a corresponding increase in the "fuel load" of the type of vegetation susceptible to more severe and frequent fires in the landscape. Another supporting perspective is provided by Matt McGlone, who's article appears in the same issue of Science. He adds that it was not the hunting of the herbivores alone that changed the ecology. "Human-lit fires, which are often targeted in space and time to have the greatest effect on vegetation, were most likely the key factor in the subsequent switch to sclerophyll," he writes[2]. But his general conclusions are much the same: "The Australasian megafaunal extinction story now seems clear. Shortly after their arrival, small bands of hunters had a devastating effect on large animals, whether it was ~41,000 years ago in Australia or ~750 years ago in New Zealand. Any climate change at those times was modest and highly unlikely to affect the outcome. Fire and massive biome disruption followed human arrival in regions where there had previously been little or no fire, such as wet tropical Queensland and eastern New Zealand.......The Australasian records clearly show that human hunting alone, on a continental scale at a time of only slight climate and vegetation change, is sufficient to eliminate megaherbivores."[2] The full report of the study can be found in the March 23, 2012 issue of the journal Science, a publication of the American Association for the Advancement of Science. [1] S. Rule, et.al.,"The Aftermath of Megafaunal Extinction: Ecosystem Transformation in Pleistocene Australia," SCIENCE VOL 335, 23 MARCH 2012. [2] Matt McGlone, "The Hunters Did It," from Perspectives, SCIENCE VOL 335, 23 MARCH 2012.
|
