The resilience that has been ‘baked in’ to the rich ecosystems shaped by big herbivores over tens of millions of years could be lost as the world approaches a new tipping point, an international team of scientists has warned.
We can learn a lot about the future health of our planet by studying its past. Now, a study in Nature Communications shows how the ecosystems curated by big herbivores, such as woolly mammoths, giant deer and bison, have changed over the last 60 million years.
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Fernando Blanco and colleagues studied the fossilised remains of more than 3,000 large herbivores from this time period and found that – for the most part - although species came and went, overall, the function of the ecosystems remained constant.
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This stability was overturned on two occasions, when physical changes disrupted the ecosystems. “Twice in the last 60 million years, the environmental pressure was so great that the entire system underwent global reorganization,” says Blanco, who was at the University of Gothenburg.
The first tipping point occurred around 21 million years ago, when shifting continents closed the ancient Tethys Sea and formed a land bridge between Africa and Eurasia. Many large plant-eaters, including ancient deer, pigs, rhinos and elephants crossed the bridge and moved into new territories, reshaping the ecological balance.
The second tipping point happened around 10 million years ago, as a changing climate led to the expansion of grasslands and the rise of grazing species with tougher teeth, and also the shrinking of forests and the disappearance of many forest-dwelling herbivores.
The variety of ecological roles played by big herbivores started to decline, yet despite these losses, the overall ecological structure of communities remained remarkably intact. Even as many of the biggest species, like mastodons and giant rhinos went extinct, the basic framework of roles within ecosystems endured.
“It’s like a football team changing players during a match but still keeping the same formation,” says Ignacio Lazagabaster from the National Research Center on Human Evolution in Burgos, Spain.
This resilience has lasted for the past 4.5 million years, enduring ice ages and other environmental crises, but the team caution that the current biodiversity crisis could eventually overwhelm the system.
As environmental change accelerates and large herbivores are lost from the globe, the ecosystems that they help to maintain are changing. Now, efforts are needed to preserve and replenish these vitally important ecosystems, as we approach a potential third tipping point.
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