For millennia, African lions ruled a seemingly boundless kingdom, a sprawling, unbroken stretch of savannah onethird larger than the continental U.S. But today, 75 percent of that vast savannah is gone, and humans are fast chipping away at what remains. And Stuart Pimm is worried.
Pimm, the Doris Duke Professor of conservation ecology at Duke’s Nicholas School of the Environment, led a comprehensive study of lion populations and habitat in Africa. The results, released this past December, are harrowing: Pimm estimates that as few as 32,000 lions live on the African savannah, down from nearly 100,000 fifty years ago. Those that remain survive in increasingly disconnected slices of habitat, hemmed in by human development.
“The word savannah conjures up visions of vast, open plains teeming with wildlife,” says Pimm. “But the reality is that massive land-use change and deforestation, driven by rapid human population growth, has fragmented or degraded much of the original savannah.”
Pimm and his colleagues used high-resolution satellite imagery, coupled with data on local human and lion populations, to map areas still favorable to the big cats. They identified only sixty-seven isolated areas of savannah across the continent with suitably low human impacts and densities. Only ten were deemed to be “strongholds,” where lions have an excellent chance of survival. Many of the strongholds are located within national parks.
“Existing maps made from low-resolution satellite imagery show large areas of intact savannah woodlands. Based on our fieldwork in Africa, we knew they were wrong,” says lead author Jason Riggio M.E.M. ’11, a former member of Pimm’s lab who is now studying at the University of California at Davis. “Using very high-resolution imagery, we could tell that many of these areas are riddled with small fields and extensive, if small, human settlements that make it impossible for lions to survive.”
The situation is particularly dire in West Africa, where human populations are growing fastest and the decline in lions is steepest. The team did not identify a single stronghold in all of West Africa, and the study estimates fewer than 500 lions remain in this region, scattered across eight isolated sites.
“Giving these lions something of a fighting chance will require substantial increases in effort,” says Andrew Jacobson M.E.M. ’10, a member of Pimm’s lab. “The next ten years are decisive for this region, not just for lions but for biodiversity, since lions are indicators of ecosystem health.”