Discovery Channel: Equator

Challenge of Change (1x5)

Air date: Aug 10, 2009

For much of the year the African Savannah bakes under the oppressive Equatorial sun. The dryness is unusual for the Equator, whose regions are often covered with dense rainforests and associated with a seasonless annual cycle. Thirty million years ago part of east Africa was torn apart. Massive volcanic activity combined to form the beginnings of what would be the Great Rift Valley. Over millions of years the valley widened and grew longer, spreading north and south for more than 4,500 kilometres. The resulting mountain ranges rose 3000 metres, blocking clouds coming from the west and creating a rain shadow over east Africa. The vegetation became drier and gradually the rainforests that once covered the continent began to disappear. In its place grasslands would develop, grasslands that would profoundly change life at the Equator forever. These Carbon 4 or C4 plants had developed a revolutionary pathway for transforming sunlight and carbon dioxide into sugars. These turbo-charged plants now feed the many species of herbivore that migrate to the Savannah each November after rains feed the drought-stricken land. The ungulates have a secret weapon that allows them to eat the tough C4 grasses: they have evolved four-chambered ruminant stomachs. The Savannah is inhabited great cats, each with their own adapted modes of predation. The leopard uses stealth and camouflage, and if the hunt is successful it will retreat to the security of the trees away from the many scavengers who inhabit the grasslands. More than any other great cat, the lion has been most shaped by living under the Equatorial sun. Lions are social rather than solitary, organised and controlled by the females while the males live on the margins of the group. The blazing sun could kill them if they overheated, so they hunt collectively in the cool of night.