Elephants. Rhinos. Hippos. People travel to Africa from all corners of the globe just to glimpse these massive vegetarian wanderers of the wilderness.

But take a good look while you can.

New research by an international team of scientists, including a Stanford biologist, suggests these and other legendary giants soon will be gone forever, wiped out by a steady march of poaching, habitat destruction and livestock grazing.

The study, published in Science Advances, the open-access online journal of Science magazine, offers the first comprehensive review of the endangerment status and key threats to the world’s largest herbivores — 74 species that grow to 220 pounds or more — as well as the consequences of their decline and actions needed to save them. Scientists found these giants are facing dramatic population declines — about 60 percent are threatened with extinction.

“Without radical intervention,” they wrote, “large herbivores (and many smaller ones) will continue to disappear from numerous regions, with enormous ecological, social and economic costs.”

Stanford biologist and study co-author Rodolfo Dirzo argues that humans will feel social and health consequences as well, in the form of higher wildfire risks and increased rodent-borne disease.

“We depend on the well-being of animal and plant life,” said Dirzo, a biologist at the Stanford Woods Institute for the Environment. “Just as we can easily think about deforestation, we should think about animal loss.”

Using information gathered from the International Union for Conservation of Nature’s Red List of Threatened Species, Dirzo and his 15 co-authors determined that 44 of the 74 species are threatened with extinction — 12 of which, including four rhinoceros species, are nearly gone.

Laurel Fox, a UC Santa Cruz ecologist who studies plant-animal interactions, said the study drives home the urgency of the crisis.

“I knew that some of this was happening, but not the extent that it’s happening,” Fox said.

Elephants are in major decline. From 2002 to 2011, forest elephant populations in central Africa dropped by 60 percent. And from 2010 to 2012, poachers killed more than 100,000 elephants — one-sixth the population of all African elephants at that time.

Most of the threatened species inhabit developing countries, such as the bearded pig in Borneo and the takin and wild yak that graze in Himalayan meadows. Strict game regulations keep large herbivores relatively stable in the U.S. and other developed nations, but these countries have fewer big mammals to begin with — mammoths and scores of other species native to Europe and the Americas were wiped out at the end of the last ice age approximately 11,000 years ago.

The biggest threat to large herbivores is hunting, bolstered by global demand for wild meat, the study found. Another contributor is illegal poaching, not just for elephant tusks but also hippo teeth, tapir feet and the okapi’s striped hide. According to a 2013 study, rhinoceros horns cost more by weight than diamonds, gold or cocaine.

These animals also suffer from habitat loss and land-use changes, from both humans and livestock.

“Domestic livestock are a direct competition to wild herbivores for forage and water,” said William Ripple, an ecologist at Oregon State University and lead author of the study. “In many places they’re edging out the wild animals.”

Meat consumption isn’t the only livestock driver — increased numbers of goats raised for cashmere are crowding out prey for snow leopards in Central Asia.

“There’s so many of these domestic livestock and the demand is so high for cashmere,” said Ripple, “that the people in the rich countries are helping fuel this decline in the wildlife.”

Large herbivores are so-called “ecosystem engineers,” their activities regulating the habitats and food sources of other wildlife. They disperse seeds, a service that helps plants colonize and maintain biodiversity. Fewer grazing herbivores also means shrubs and forests can take over grasslands, restricting other herbivores’ habitats and reducing food for predators.

“The big humbling lesson here is that nature is very much interconnected,” said Ripple. Without large herbivores, “the whole fabric of the ecosystem becomes less resilient and doesn’t function as well.”

Preventing further loss, the authors wrote, will require global efforts to increase protected areas and manage poaching. To Dirzo, conserving is everyone’s responsibility.

“It took about 3.5 billion years of evolution to come to this wonderful biodiversity,” he said. “So, ethically and morally, that’s a very important factor that one needs to take into account.”

Contact Kerry Klein at kklein@mercurynews.com. Follow her at Twitter.com/EineKleineKerry