According to a new study led by Prof William Ripple of Oregon State University, many populations of large plant-eaters such as elephants, bison, rhinoceroses, zebras, camels and tapirs are diminishing or threatened with extinction in grasslands, savannahs, deserts and forests.
African elephants at the Amboseli national park near Mount Kilimanjaro. Image credit: Amoghavarsha / CC BY-SA 3.0.
Prof Ripple and co-authors focused on 74 large herbivore species with mean adult body masses more than 100 kg.
These largest species represent four orders (Proboscidea, Primates, Cetartiodactyla, and Perissodactyla) and eleven families (Elephantidae, Rhinocerotidae, Hippopotamidae, Giraffidae, Bovidae, Camelidae, Tapiridae, Equidae, Cervidae, Suidae, and Hominidae). Most of these species are entirely herbivorous, but some are generalists.
The team reviewed how the combined impacts of hunting, encroachment by humans and their livestock, and habitat loss could lead to the extinction of these animals relatively soon.
“I expected that habitat change would be the main factor causing the endangerment of large herbivores. But surprisingly, the results show that the two main factors in herbivore declines are hunting by humans and habitat change. They are twin threats,” said Prof Ripple, who is the senior author on a paper in the journal Science Advances.
He and his colleagues refer to a 1992 study of the decline of animals in tropical forests. The author, Dr Kent Redford of the University of Florida, first used the term ‘empty forest.’ But Prof Ripple’s team went a step further.
“Our analysis shows that it goes well beyond forest landscapes to savannahs and grasslands and deserts. So we coin a new term, the empty landscape,” Prof Ripple said.
The highest numbers of threatened large herbivores live in developing countries, especially Southeast Asia, India and Africa.
Only one endangered large herbivore lives in Europe – the European bison (Bison bonasus), and none are in North America, which has already lost most of its large mammals through prehistoric hunting and habitat changes.
According to the scientists, 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. Meanwhile, herbivore hunting occurs for two major purposes – meat consumption and the global trade in animal parts. An estimated 1 billion humans subsist on wild meat.
“Organized crime is facilitating a dramatic decline of elephants and rhinoceros in parts of Africa and southern Asia, reversing decades of conservation accomplishments. Poaching and illegal trade in elephant products are currently the top threats to elephants,” the scientists said.
“Ivory poaching has surged in recent years, largely due to a rise in demand for and price of ivory in China. The number of forest elephants (Loxodonta africana cyclotis) in central Africa declined by 62% between 2002 and 2011.”
“Currently, 75% of elephant populations are declining and at risk of extirpation, and the range of elephants has drastically declined. More than 100,000 African elephants were poached during the 3-year period from 2010 to 2012. This level of illegal kills represents 20% of the current estimated population size of 500,000 African elephants, and even populations of savanna (or bush) elephants (Loxodonta africana africana) are now declining.”
“Poaching of rhinoceros for their horns has also soared in recent years because of its use in traditional Chinese medicine. The number of rhinoceros poached in South Africa grew by two orders of magnitude from 13 in 2007 to 668 in 2012 and 1,004 in 2013. The situation is so desperate that an emergency intervention is planned in which large numbers of white rhinoceros will be translocated out of South Africa’s Kruger National Park and placed in potentially more secure areas.”
“Furthermore, at least in part due to poaching, Africa’s western black rhinoceros (Diceros bicornis longipes) was declared extinct in 2011.”
“This slaughter is driven by the high retail price of rhinoceros horn, which exceeds, per unit weight, that of gold, diamonds, or cocaine.”
“The loss of large herbivores suggests that other parts of wild ecosystems will diminish. 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” Prof Ripple said.
“We hope this report increases appreciation for the importance of large herbivores in these ecosystems. And we hope that policymakers take action to conserve these species,” Prof Ripple concluded.
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William J. Ripple et al. 2015. Collapse of the world’s largest herbivores. Science Advances, vol. 1, no. 4, e1400103; doi: 10.1126/sciadv.1400103
