This documentary shows how wild creatures help to build the very foundations upon which environments depend. In North America, herds of bison maintain the prairies that used to spread across the continent, while in Africa giraffes work as tree pruners and help maintain the savanna grasslands that the greatest herds on earth depend upon. In Australia, the cuddly koala and the eucalypt forests have maintained a balance that is now being altered, while the wombat helps to sustain plant life in the arid interior and the cassowary virtually chooses the plants that will grow in the tropical forests in the north of the continent. In Africa, the great migrations play a crucial role in the health of the grasslands, and the final act of clearance by vultures and dung beetles is at the very heart of the cycle of life and death….