Economics: What are the costs and benefits of such actions that can save elephants?

Elephants eat 300 pounds of food per day. They flourished in Africa whenthey could roam over huge areas of land, eating the vegetation in one area andthen moving on so that the vegetation could renew itself. Now, the area overwhich elephants can roam is declining. Without some action, the elephants willbecome extinct. What actions might save the elephants? What are the costs andbenefits of such actions?