Global decline of large herbivores may lead to an 'empty landscape'

http://www.eurekalert.org/pub_releases/2015-05/osu-gdo042715.php

Public Release: 1-May-2015
Oregon State University

The decline of the world's large herbivores, especially in Africa and parts of Asia, is raising the specter of an "empty landscape" in some of the most diverse ecosystems on the planet, according to a newly published 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, scientists say.

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The authors focused on 74 large herbivore species - animals that subsist on vegetation - and concluded that "without radical intervention, large herbivores (and many smaller ones) will continue to disappear from numerous regions with enormous ecological, social, and economic costs." Ripple initiated the study after conducting a global analysis of large-carnivore decline, which goes hand-in-hand, he said, with the loss of their herbivore prey.

"I expected that habitat change would be the main factor causing the endangerment of large herbivores," Ripple said. "But surprisingly, the results show that the two main factors in herbivore declines are hunting by humans and habitat change. They are twin threats."

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The highest numbers of threatened large herbivores live in developing countries, especially Southeast Asia, India and Africa, the scientists report. Only one endangered large herbivore lives in Europe (the European bison), and none are in North America, which, the authors add, has "already lost most of its large mammals" through prehistoric hunting and habitat changes.

The authors note that 25 of the largest wild herbivores now occupy an average of only 19 percent of their historical ranges. Competition from livestock production, which has tripled globally since 1980, has reduced herbivore access to land, forage and water and raised disease transmission risks, they add.

Meanwhile, herbivore hunting occurs for two major purposes, the authors note: meat consumption and the global trade in animal parts. An estimated 1 billion humans subsist on wild meat, they write.

"The market for medicinal uses can be very strong for some body parts, such as rhino horn," said Ripple. "Horn sells for more by weight than gold, diamonds or cocaine." Africa's western black rhinoceros was declared extinct in 2011.

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The loss of large herbivores suggests that other parts of wild ecosystems will diminish, the authors write. The likely consequences include: reduction 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; changes in habitat for smaller animals including fish, birds and amphibians.

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