DINOKENG GAME RESERVE, South Africa — The male lion brushes through the tall grass and strides into a clearing in a South African wildlife sanctuary. A man beckons the big cat with purring sounds. The lion, Bayetsi, responds with a gentle growl and caresses Kevin Richardson, popularly known as the “lion whisperer,” with its mane. Richardson hopes his hands-on stunts with lions will highlight the plight of the African predator, whose numbers have dwindled.