Habitat and Niche

The habitat of an organism is simply its address -- the actual physical place, characterised by a specific set of abiotic and biotic conditions, where that organism naturally lives. A frog's habitat may be a freshwater pond; a tiger's habitat is a particular type of forest; a barnacle's habitat is the intertidal rocky shore. Habitat answers the question "where does it live?"

The niche, by contrast, answers a very different and much richer question -- "what does it do there, and how does it live?" The ecological niche of a species is often described as its "occupation" or functional role within the community: it summarises everything about how the species interacts with its environment, including what it eats and what eats it (its trophic position and food habits), where and how it breeds, the range of physical conditions (temperature, humidity, pH, and so on) it can tolerate, the resources it uses, and the times of day or seasons at which it is active. Two species can share exactly the same habitat -- the same pond, the same forest canopy -- while occupying two quite different niches, because they differ in diet, activity pattern, or the precise resource they exploit.

Ecologists further distinguish between the fundamental niche, which is the full range of conditions and resources a species is theoretically capable of using in the total absence of competition or interference from other species, and the realised niche, which is the narrower portion of that fundamental niche the species actually occupies in nature once the effects of competitors, predators, and other biotic pressures are taken into account. In the real world, a species is almost always squeezed into some subset of its fundamental niche by the other organisms sharing its habitat -- so the realised niche is typically smaller than the fundamental niche. …