Herbivores like rhinos and tortoises face greater risk of extinction than predators, reveals analysis

Invasive animals, pollution, and habitat alteration take a higher toll on herbivores, say researchers


                            Herbivores like rhinos and tortoises face greater risk of extinction than predators, reveals analysis
(Edd Hammill)

Scientists have observed a pattern over the last 500 years: more plant-eating animals have been going extinct than carnivores. While predators still face a risk of getting wiped out, they might not be as susceptible as the herbivores such as the rhinos or tortoises, a new analysis found.

For long, ecologists assumed that predators face the highest risk. But when Trisha Atwood and her colleagues from Utah State University examined the data, they were taken by surprise. "The data consistently showed that herbivores, not predators, were at the greatest risk of extinction, as well as they had the highest proportion of extinctions in the recent past (past 500 years) and in the late Pleistocene [the Last Ice Age epoch]," Atwood, the lead author of the study, told MEA WorldWide (MEAWW).

Human actions -- either through hunting or destruction of forests -- drove most of 368 vertebrate species into extinction over the last five centuries. The researchers calculated that about 25% of the herbivores are at risk of going extinct, as opposed to 17.4% of the predators and 15.8% of omnivores.  

Atwood and her team combed through previous data and gathered information on the diet for over 24,500 living and extinct animal species. They wanted to determine which group of animals are more threatened than the others. The team also compared the rate of extinctions between the current species and the late Pleistocene groups.

(Edd Hammill)

What makes herbivores susceptible?

Invasive animals, pollution, and habitat alteration take a higher toll on herbivores. For instance, rats and fire ants have pushed several reptiles into extinction, the researches said. Further, body size could also play a part in making some animals more vulnerable than others.

"Larger animals tend to be more threatened with extinction than smaller ones. In general, herbivores that live on land tend to be larger than predators and omnivores," she explained. "We could not find a clear answer to why they [plant eaters] are more susceptible."

Some questions still need answers, including understanding the link between animal diet and extinction risk. The next big step, Atwood said, is to look at species' traits and different stressors and their role in driving this trend in herbivores. 

The study calls for urgent action. When large-bodied herbivores went extinct one million years ago, it led to changes on Earth. It altered plant life, changed the patterns and intensity of wildfires, and cooled the planet slightly. "Already the consequences of declines in modern herbivores from land-use change and hunting have begun to echo those that occurred then," she noted. "We must redouble our efforts to strategically invest in conservation and management of herbivores to avoid future dramatic changes in the functions arising from animals at the base of global food webs."

The study focused mainly on land-dwelling vertebrates, barring seabirds, and marine mammals. Future studies can look at risks faced by ocean creatures. "We also want to emphasize that our study does not suggest that predators are not in trouble. There are still thousands of predatory species out there that are threatened," she said.

The study was published in Science Advances.

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