Take the time to view this TED talk by Alan Savoury on Holistic Management. It challenges the current orthodoxy, that paints grazing animals as a negative influence on the environment. This is bio-mimicry in action.
One of the key methodologies of organic farming, is the tight integration of animals with plants into the farming system. The environment cannot exist on plants alone. In a planned environment such as a farm domestic and wild animals play a huge role in maintaining fertility and overall health.