Scientists fear that the decline of the world's largest herbivores, especially in Africa and parts of Asia, could lead to an "empty landscape" in some of the most diverse ecosystems on the planet, according to a new study.
Many populations of animals such as rhinoceroses, zebras, camels, elephants and tapirs are diminishing or threatened with extinction in grasslands, savannahs, deserts and forests.
After studying 74 of the largest herbivore species - those that weigh more than 220 pounds on average - the researchers found that "without radical intervention, large herbivores (and many smaller ones) will continue to disappear from numerous regions with enormous ecological, social, and economic costs."
"I expected that habitat change would be the main factor causing the endangerment of large herbivores," lead author William Ripple from Oregon State University said in a statement. "But surprisingly, the results show that the two main factors in herbivore declines are hunting by humans and habitat change. They are twin threats."
While trees and other vegetation may exist, plant-eating animals need more than just that to survive. According to the researchers, the loss of forest fauna alone poses a long-term threat to ecosystems on which herbivores rely.
"Our analysis shows that it goes well beyond forest landscapes," Ripple said, "to savannahs and grasslands and deserts. So we coin a new term, the empty landscape."
Out of the 4,000 species of known terrestrial herbivores, which inhabit every continent except Antarctica, those found in developing countries like Southeast Asia, India and Africa are most threatened by habitat loss.
Astonishingly, 25 of the largest wild herbivores now occupy an average of only 19 percent of their historical ranges.
And thanks to competition from livestock production - which has tripled globally since 1980 - herbivores can't access land, forage and water in some areas. Not to mention livestock has put them at a higher risk of contracting transmitted diseases. (Scroll to read on...)
Meanwhile, herbivore hunting is still a huge issue. Wanted for their meat and animal parts, herbivores are being hunted into near extinction.
For example, it's no secret that rhinos are dying in record numbers due to poaching for their valuable horns.
"The market for medicinal uses can be very strong for some body parts, such as rhino horn," Ripple explained. "Horn sells for more by weight than gold, diamonds or cocaine."
Africa's western black rhinoceros was declared extinct in 2011, and the white rhino doesn't seem to be far behind, with only five left in the entire world.
In addition, the causes of the decline of some large herbivores "are difficult to remedy in a world with increasing human populations and consumption."
In fact, an estimated one billion humans subsist on wild meat, researchers say.
"But it's inconceivable that we allow demand for horns and tusks to drive the extirpation of large herbivores from otherwise suitable habitat," co-author Taal Levi said. "We need to intensify the reduction of demand for such items."
What's more, these findings are not only bad news for large herbivores, but also for other animals and plants around the world as well. That's because the loss of large herbivores suggests that other parts of wild ecosystems will diminish, too.
This includes a decline in food for large carnivores such as lions and tigers, diminished seed dispersal for plants, more frequent and intense wildfires, slower cycling of nutrients from vegetation to the soil, and changes in habitat for smaller animals such as fish, birds and amphibians.
"We hope this report increases appreciation for the importance of large herbivores in these ecosystems," Ripple concluded. "And we hope that policymakers take action to conserve these species."
The findings were published in the journal Science Advances.
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