Why big animals can’t take a little rain
Giant sloths and saber-toothed tigers, oh my
Melting from glaciers and permafrost was not kind to the large animals of the last Ice Age.
The persistent moisture turned grasslands into peatlands and bogs, a less than ideal habitat for huge grazers. As their world grew wetter, many of these megafaunal animals across Eurasia and the Americas became extinct.
Today, climate change is fueling heavy precipitation around the globe. Species have started to shift locations or find other ways to adapt. Is the past prologue?
“Predicting specifics about the future is really hard for such a dynamic system,” said Tim Rabanus-Wallace, a researcher at the University of Adelaide and lead author of a new study published in the journal Nature Ecology and Evolution that examines the impact of moisture on the megafaunals who lived some 11,000 years ago. But, “we can certainly see that soil moisture is expected to increase in various places around the globe” as a result of global warming.
The researchers, from the Australian Centre for Ancient DNA (ACAD) of the University of Adelaide, determined the age of 511 bones from animals such as bison, horses, and llamas to study the role of environmental changes in the extinction of large land creatures such as giant sloths and sabre-toothed cats.
“We didn’t expect to find such clear signals of moisture increases occurring so widely across all of Europe, Siberia, and the Americas,” said Alan Cooper, the study leader and director of the ACAD. “The timing varied between regions, but matches the collapse of glaciers and permafrost and occurs just before most species go extinct.”
The scientists, including those from the University of Alaska Fairbanks, the University of Oslo, the Yukon government and paleontologists from Russia and Canada, measured nitrogen isotopes preserved in ancient animal bones recovered from Europe, Siberia, and North and South America. They discovered signs of enormous increases in moisture.
Matthew Wooller of the University of Alaska Fairbanks, another author of the study, noted that climate changes occurred at different times on different continents, “but they all showed that moisture increased massively just prior to extinction. The really elegant feature of this study is that it produces direct evidence from the fossils themselves. These extinct creatures are informing us about the climate they experienced leading up to their own extinctions.”
The results also explain why Africa experienced a much lower rate of megafaunal extinctions. “Africa’s position across the equator means that grassland zones have always surrounded the central monsoon region,” Cooper said. “The stable grasslands are what has allowed large herbivores to persist.”
To be sure, the summer monsoon season typically brings torrential rains. But in Africa, “the top and bottom are very dry, so they are deserts,” Rabanus-Wallace explained. Grassland “tends to form a sort of border around the jungle. When the climate changes, the monsoon region or the deserts can grow or shrink, but the grasslands just follow the desert-jungle boundary as it moves up and down.”
He predicts that, in the near future, some regions—like the prairies of Northern North America, the Eurasian Steppes, and the Pampas in South America — could find their semi-arid grassland reserves overrun by more moisture-adapted shrubs and trees. “It’s impossible that this won’t contribute to some extinctions” he said. The greatest danger may be to food-growing environments.
“What climate change once did to the megafaunal community, it may proceed to do to our food economy,” Rabanus-Wallace said. “In such scenarios it tends to be those most in need who suffer.”
Paradoxically, “on long, geological timescales, animals as physically large as humans tend to go extinct quite rapidly,” he said. “However, in my opinion, this rule could be bucked by humans because of our uniqueness. We are the greatest ecosystem engineers evolution has ever produced, with absolutely no analog. Long-surviving life forms tend to either inhabit a static environment, like sharks or crocodiles, or be highly adaptable, like insects or plants.”
Since the former is no longer an option, “we need to harness our immense capability for the latter,” he added.
“In terms of climate and ecological change, this means having the ability to build energy infrastructure quickly and cheaply, using tech that can suit a wide range of environments,” he says. It also means disseminating ways for farmers “to switch their production where needed to suit the environment.”
Marlene Cimons writes for Nexus Media, a syndicated newswire covering climate, energy, policy, art and culture.