in part due to the careful management. The population is controlled because if you let it get out of hand they kill too many duiker, kudu, springbok, and whatever else they eat. When too many of those are killed the lions are left without food and the they die off in a major way. Yes man's impact is one of the reasons that animal populations have to be managed. This is more true in Africa as we are not even a generation away from some indigenous peoples using game as a primary food source.

It's really the same as managing wildlife populations anywhere.