February 6, 2014
Change In Vegetation Killed Off Large Mammals After The Last Ice Age
[ Watch the Video: Diet Changes Killed Off Woolly Mammoths ]
Brett Smith for redOrbit.com - Your Universe OnlineScientists have put forth many theories on why woolly mammoths and other large animals went extinct around 10,000 years ago, from the devastating effects of a comet impact to overhunting by humans.
A new DNA-based study published in the journal Nature has found that the flowering plants these “megafauna” depended on disappeared from northern Asia and North America after the last Ice Age – robbing the massive animals of a vital food source.
Instead of grasslands dominating the northern hemisphere, landscape was far more diverse and stable than today’s steppes, with megafauna like woolly rhinos and mammoths feeding on grasses and protein-rich flowering plants, or forbs. However, between 25,000 and 15,000 years ago, during the last Ice Age, a major loss of plant diversity took place, the study authors said.
“We knew from our previous work that climate was driving fluctuations of the megafauna populations, but not how,” said study author Eske Willerslev, a director at the Centre for GeoGenetics at the Natural History Museum of Denmark. “Now we know that the loss of protein-rich forbs was likely a key player in the loss of the ice age megafauna.”
To reach their conclusion, the study team sampled permafrost cores dating back 50,000 years from 17 spots in northern Russian, Canada, and Alaska. They discovered that DNA signatures inside the cores show that flowering species, and the tiny roundworms connected with them living in the soil, were more prevalent than grasses on the ancient steppes.
The team also analyzed 18 archival samples of stomach contents and feces from mammoths, woolly rhinos, horses, reindeer, and elk. They discovered that flowering species were a significant portion of these animals' diet.
“We show that the permafrost contains a vast, frozen DNA archive left as footprints from past ecosystems, and that we can dechiffer this archive by exploring the collections of plants and animals stored in Natural History Museums,” said study author Christian Brochmann, a botanist at the Natural History Museum at the University of Oslo in Norway. “Using DNA from museum collections as reference, we could identify the different plant species that co-occurred with extinct ice age mammals.”
The new study expanded on the same groups from 2011 where the scientists indicated that climate is the reason for the mass extinction of a number of the large mammals. However, the 2011 study lacked a “smoking gun,” the researchers said. Now, the new study data indicated that the likely reason for the mass extinction of the large mammals after the latest Ice Age is the shifts in the vegetation.
Willerslev warned that the study could be an indicator of the consequence awaiting us if we fail to get climate change under control.
“Interestingly one can also see our results in the perspective of the present climate changes. Maybe we get a hold on the greenhouse gases in the future,” he said. “But don't expect the good old well-known vegetation to come back when it becomes cooler again after the global warming. It is not given that the 'old' ecosystems will re-establish themselves to the same extent as before the warming. It's not only climate that drives vegetation changes, but also the history of the vegetation itself and the mammals consuming it.”