The Ngorongoro area is part of the Serengeti ecosystem, and to the north-west it adjoins the Serengeti NP and is contiguous with the southern Serengeti plains. These plains also extend to the north into the unprotected Loliondo division and are kept open to wildlife through transhuman pastoralism practiced by Masai. The south and west of the area are volcanic highlands and the southern and eastern boundaries are approximately defined by the rim of the Great Rift Valley wall, which also prevents animal migration in these directions.