The ancient ecosystems curated by the world’s big herbivores have only been through two major upheavals in the last 60 million years, a study in Nature Communications has found. This suggests that these ecosystems are hardy, but researchers now caution that a third, human-driven tipping point could threaten that resilience.
Ecosystems are made up of communities of living things, and the physical environment they live in. Large herbivores, such as mastodons and giant deer, have been helping to shape these ecosystems for many millions of years.
Scientists were interested in how these herbivore-dominated ecosystems changed over time, so they analysed the fossil remains of over 3,000 large herbivores spanning 60 million years.
Extinctions are part of life on earth, so it was no surprise that species came and went. What was surprising, however, was that the ecosystems that the animals were part of remained remarkably stable.
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“It’s like a football team changing players during a match but still keeping the same formation,” says Ignacio A. Lazagabaster from the National Research Center on Human Evolution in Burgos, Spain. “Different species came into play and the communities changed, but they fulfilled similar ecological roles, so the overall structure remained the same.”
This stability was punctuated by two episodes that shook things up.
The first major change occurred around 21 million years ago, when a land bridge opened up between Africa and Eurasia. This unleashed a wave of migrations that reshaped ecosystems across the world. The ancestors of modern elephants, which had evolved in Africa, started to spread into Europe and Asia, whilst deer, pigs, rhinos and other large herbivores also expanded their range.
The second change happened 10 million years ago, as the Earth’s climate became cooler and drier. As grasslands expanded and forests declined, there was a rise in grazing and browsing species, and a decline in forest-dwelling herbivores.
Now a third shift may be underway.
"Our results show that ecosystems have an amazing capacity to adapt. But the rate of change is so much faster this time. There's a limit. If we keep losing species and ecological roles, we may soon reach a third global tipping point, one that we're helping to accelerate, " says Juan Cantalapiedra from the National Museum of Natural Sciences in Madrid.
Ecosystems could cease to function as they used to, so work is needed to preserve or reintroduce species that could help to maintain their integrity.
