1. the ultimate unit of the habitat, i.e., the specific spot occupied by an individual organism 2. by extension, the more or less specialized relationships existing between an organism, individual or synusia, and its environment 3. the specific set of environmental and habitat conditions that permit the full development and completion of the life cycle of an organism —note the ecological niche of a species is the functional role of the species in a community; the fundamental niche is the totality of environmental variables and functional roles to which a species is adapted; the realized niche is the niche a species normally occupiesThis definition last updated 07/21/2008