Everybody knows the haunting tune and those words: "In the jungle, the mighty jungle, the lion sleeps tonight." The song is a reminder of the power of the wilderness and of the awe it can make us feel even across oceans and at the other end of the earth. What West Africa’s lions are facing today, though, is the big sleep—that is, extinction.

Researchers who spent six years scouring protected areas in the 11 West African nations where lions were once at home found evidence of fewer than 250 surviving adult lions. Think of it this way: That’s smaller than the high school student body in my small town in New England, distributed across an area longer than the distance from Portland, Maine, to Jacksonville, Fla.

It’s not just West Africa: Lion populations are in dramatic decline across the continent. In Kenya, where they are the symbol of national strength and an essential factor in the tourist economy, biologists have predicted that lions will disappear from the wild within just 15 years. Continent-wide, the rapidly dwindling population is down to about 35,000 lions in 67 isolated pockets.

Until the new study, published in the journal PLOS One, scientists had paid hardly any attention to West Africa’s distinctly different lions, which are more closely related to a remnant subspecies in India than to lions in eastern and southern Africa. They began the research for the new study in 2006, following pug marks through the forest, monitoring camera traps, and occasionally playing sounds of a lion roaring and listening for a response, almost always in vain. If it was a jungle out there, it was a largely empty one.

The study concludes that West Africa’s lions are in a “catastrophic collapse,” hanging on in just five nations. The news is even worse than that sounds: Almost 90 percent of the lions live in a single trans-frontier population on the shared borders of Benin, Niger, and Burkina Faso, making them highly vulnerable to political upheaval, poaching, or an outbreak of disease. The other surviving lions are in Nigeria and Senegal. In some of these countries, parks exist on paper only, without staff or budget.

The discouraging news about lions came in the same week as another study showing a dramatic decline in almost all of the largest carnivore species worldwide. The authors of that paper, published in Science, looked at 31 predator species and found three-quarters of them are in decline, including leopards, cheetahs, polar bears, tigers, giant otters, and multiple wolf species. The usual killer is loss of habitat from rapidly expanding human populations, combined with persecution by humans.

“Globally, we are losing our large carnivores,” said lead author William Ripple, an ecologist at Oregon State University. “Many of these animals are at risk of extinction, either locally or globally. And, ironically, they are vanishing just as we are learning about their important ecological effects.”

Over the past few decades, scientists have turned up increasing evidence that losing top predators can cause entire ecosystems to collapse, with humans among the potential victims. The 1926 eradication of wolves from Yellowstone National Park, for instance, caused the elks on which they preyed to proliferate, turning the park into a glorified ranch, nibbled down to dirt in many places. The loss of wolves changed not just the look of the land but the quality of streams and the ability of other species to survive there. Biologists refer to those knock-on effects as “a trophic cascade.”

But since reintroduction of the wolves in 1995, Ripple’s research has shown that elk numbers and behavior have changed, aspen and willow have grown back on the banks of creeks, birds and amphibians have returned, and even fish have benefited from the ponds created by beavers.

Trophic cascades are now taking place worldwide, according to the new study. Though people in West Africa kill lions to protect their livestock, for instance, that has allowed olive baboons, a prey species, to expand—causing the strategy to backfire. “Among large mammals,” the new study reports, “baboons pose the greatest threat to livestock and crops and they use many of the same sources of animal protein and plant foods as humans in sub-Saharan Africa. In some areas, baboon raids in agricultural fields require families to keep children out of school so they can help guard planted crops.” That is, they would have been better off with the lions.

Some studies also suggest that loss of predators, and the resulting increase in rodents and other prey species, can put humans at risk of disease. About 60 percent of all human diseases originally came from animals—as do 75 percent of emerging diseases such as Lyme disease and Ebola. The scientific evidence is mixed so far, but in ridding ourselves of the nuisance of predators, humans may turn out to have made a deadly mistake.

The new study sees hope, surprisingly, from Europe, one of the first places on the earth where humans hounded big predators into oblivion. A recent paper by the Zoological Society of London found that lynx, golden jackals, brown bears, and wolverines are all on the rebound there. That success has largely depended on the abandonment of marginal lands by small farmers and herders in Europe—while in much of the developing world, the opposite is still under way. A key step to change that is to reduce human population growth, which the study describes as “one of the most insidious threats to carnivores.”

The authors of the new study in Science conclude, “It will probably take a change in both human attitudes and actions to avoid imminent large-carnivore extinctions. A future for these carnivore species and their continued effects on planet Earth’s ecosystems may depend upon it.”

They’re not alone: Our survival may hang in the balance.