The driving off or depletion of animal life in a geographical area or areas: Defaunation is considered to be one of the world's most significant global changes, on par with environmental changes like global warming, deforestation, and shifts in the nitrogen cycles.

Defaunation, or animal impoverishment, is usually missing from the analyses of tropical forest conservation that results from human activities which include deforestation and the loss of the fauna, particularly the medium and large animals that are the most vulnerable, because of hunting or habitat reduction or fragmentation of forests.