JOHANNESBURG — The lions that roam Africa’s savannahs have lost as much as 75 percent of their habitat in the last 50 years as humans overtake their land and the lion population dwindles, said a study released Tuesday.

Researchers at Duke University, including prominent conservationist Stuart Pimm, warned that the number of lions across the continent has dropped to as few as 32,000, with populations in West Africa under incredible pressure.