Two big events shaped the herbivores during 60 million years but their role remains

(Press-News.org) Two major environmental shifts have triggered global transformations in large herbivore communities. A new study with researchers from the University of Gothenburg show how these ecosystems remained remarkably resilient despite extinction and upheaval.

From mastodons to ancient rhinos and giant deer, large herbivores have been shaping Earth’s landscapes for millions of years. A new study, published in Nature communications, shows how these giants responded to dramatic environmental shifts – and how their ecosystems found ways to stay together, even as species disappeared.

An international team of scientists analyzed fossil records from over 3,000 large herbivores across 60 million years.

“We found that the large herbivores ecosystems stayed remarkably stable over long periods of time, even as species came and went,” said Fernando Blanco, leading author and a researcher at the University of Gothenburg at the time. “But twice in the last 60 million years, the environmental pressure was so great that the entire system underwent global reorganization.”

Two major global shifts

The first major change occurred around 21 million years ago, when shifting continents closed the ancient Tethys Sea and formed a land bridge between Africa and Eurasia. This new land corridor unleashed a wave of migrations that reshaped ecosystems across the globe.  Among the travelers were the ancestors of modern elephants, which had evolved in Africa and now began to spread across Europe and Asia. But deer, pigs, rhinos, and many other large plant-eaters also moved into new territories, altering the ecological balance.

The second global shift came around 10 million years ago, as Earth’s climate became cooler and drier. Expanding grasslands and declining forests led to the rise of grazing species with tougher teeth and the gradual disappearance of many forest-dwelling herbivores. This marked the beginning of a long, steady decline in the functional diversity of these animals – the variety of ecological roles they played.

Fewer species, same structure

Despite these losses, the researchers found that the overall ecological structure of large herbivore communities remained surprisingly stable. Even as many of the largest species, like mammoths and giant rhinos, went extinct in the last 129,000 years, 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,” said Ignacio A. Lazagabaster, researcher at CENIEH in Spain and co-author of the study. “Different species came into play and the communities changed, but they fulfilled similar ecological roles, so the overall structure remained the same.”

Third tipping point

This resilience has lasted for the past 4.5 million years, enduring ice ages and other environmental crises up to the present day. However, the researchers caution that the ongoing loss of biodiversity – accelerated by human activity – could eventually overwhelm the system.

“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 L. Cantalapiedra, researcher at MNCN in Spain and senior author of the study.

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