Unless we sort out how we feed the growing human population, thousands of birds and mammals will face the specter of extinction in coming decades, according to a new study published June 1st in the journal Nature.
"With so many people on Earth now, and the numbers increasing by another three or four billion before we finally level off at our carrying capacity, the impact on extinctions is really great," says lead author David Tilman.
Tilman, an ecologist at the University of Minnesota, and his colleagues looked at the data for the world's "threatened" birds and mammals, which they defined as the vulnerable, endangered or critically endangered animals on the International Union for Conservation of Nature's Red List of Threatened Species. They also pinpointed where these animals occurred, homing in primarily on the biodiverse tropics in Southeast Asia, sub-Saharan Africa, and South America. These regions are also experiencing—or are poised to experience—huge upticks in human populations and wealth.
The team found that 80 percent of these animals owed their threatened status to the loss of their habitat for agriculture. And the killing of animals has brought the survival of 40 to 50 percent of these species into question. Often, that hunting is for meat, but the trade in body parts, such as rhinoceros horn or ivory from elephants, takes a substantial toll.
But the thrust of their work wasn't just to identify these trends, which Tilman says weren't all that surprising.
"I'm not unique among ecologists in warning that we are in the midst of an extinction event," he says. Study after study has shown that we're in the midst of a sixth great extinction. "My goal in starting to do these analyses was to try to find pathways toward some kind of a solution."
Without a concerted effort to stop clearing forests and other wildlife habitats to meet our nutritional needs, the trend toward extinction will continue, he says, especially with an increase of 3.2 billion people to Earth's population by 2060.
"People will win out over any other organism," Tilman says. "It's hard for large species to live around humans because humans take up so much of their habitat and break it into little pieces."
But changes to the way we churn out food for those additional mouths could be hugely beneficial for biodiversity, particularly in developing economies where yields are far below what they could be, the researchers argue in the paper.
If farmers cut fertilizer use by 25 percent, they would still wind up producing about the same amount of food.
"A dollar invested in increasing yields in a typical African country gives $3 to $4 of more food," Tilman says.
Similarly, habitat disruptions such as water pollution could be avoided in developed countries like the United States if we can better time the applications of "inputs" such as fertilizer. If farmers cut its use by 25 percent, they would still wind up producing about the same amount of food, the authors write.
They advocate the inclusion of these concerns in conservation as a way of stopping the need for habitat destruction, before it cascades into the steep declines in wild animal populations seen recently. And Tilman says turning that trend around will require a shift in how we deal with threatened species.
Currently, he says, "our actions are viewed as having no impact until we finally push a species to the brink of extinction, which then puts it on our endangered species list, at which time we start paying attention to it."
Scientists have managed to save animals such as the critically endangered California condor from extinction, and they've successfully reintroduced the Arabian oryx back into the wild, which is now listed as vulnerable by the IUCN. Tilman doesn't see those sorts of approaches as sustainable for all of the world's threatened species, however.
"Every [species] that we've saved has been a wonderful achievement, but it has taken immense effort," Tilman says. "We don't have the money to babysit ... tens of thousands of species around the world."
Limited resources combined with the rate at which the number of people is increasing makes the need for solutions especially urgent, he added.
"It's this last big burst of growth and human influence on the Earth, and what we do now is going to determine forever the kind of world we have," Tilman says. "It's crunch time for biodiversity."
This story originally appeared at the website of global conservation news service Mongabay.com. Get updates on their stories delivered to your inbox, or follow @Mongabay on Facebook, Instagram, or Twitter.