In its simplest sense, a habitat is where an organism lives and thus is a concrete physical location like a stand of trees or a pool of water. A broader concept of habitat encompasses the general set of living and nonliving features typical of a particular environment, for example, "desert habitat" or "coral reef habitat."
Ecologists can measure environmental conditions where a species normally occurs to define its habitat more rigorously. Appropriate habitat can be defined in terms of its temperature regime, the availability of light and water, the chemical environment (acidity, salinity), and the strength of physical forces (waves, wind). Species can vary substantially in the suite of environmental conditions that they tolerate and can be classified as flexible habitat generalists or narrow habitat specialists.
Ecologist G. Evelyn Hutchinson developed the related concept of the species niche , which is a "living space" delineated by the entire range of environmental conditions that an organism can tolerate and by all the resources it requires for survival, growth, and reproduction. The niche of a species is where it lives and what it does. A cactus, tarantula, and roadrunner may share a common desert habitat, but each occupies a unique niche.
Cynthia A. Paszkowski
Krohne, David T. General Ecology. New York: Wadsworth Publishing, 1997.