Both fundamental and realized niches refer to the environmental position that species occupy in an ecosystem. Fundamental niches represent all the environmental conditions where a species is able to live, and the realized niche is where the species actually lives. Other names for these niches are precompetitive and postcompetitive, respectively. In a fundamental niche, an organism can take advantage of all the biotic and abiotic factors in an ecosystem without competition from other species or pressure from predators. This niche narrows when other organisms arrive and there is competition for food and breeding partners or when predators start hunting in the area. The organism will survive if it adapts to the new conditions of its realized niche.

Fundamental niches are the same size or larger than realized niches. Also, the same species living in different locations may have different realized niches depending on the competitors and predators that are present. Fundamental and realized niches can be wide or narrow. Specialist species is the term for organisms that live in narrow niches because they thrive only in certain environmental conditions or eat a certain food. Conversely, generalist species occupy wider niches and make use of a variety of resources and can live in many different environmental conditions. The niche that an organism occupies may change dramatically over the course of its life. An example of this is when a tadpole which is an herbivore, undergoes metamorphosis into a carnivorous frog.

Comparison Chart

Fundamental Niche Realized Niche
Where the organism lives No Yes
Size Large Small
Competition for resources, predators are present No Yes
Other terminology Precompetitive niche Postcompetitive niche


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  • Ecological Niche. (n.d.). In Wikipedia. Retrieved December 27, 2017 from