How might an ecologist test whether a species is occupying its realized or its fundamental niche?

Fundamental niche is the maximum theoretical inhabited hypervolume which a species can occupy in the absence of interactions with other species on the other hand the portion of fundamental niche that a species actually exploits as a result of interactions with other species is called as realized niche.

Explanation:

In, fundamental niche the full range of environmental variables and resources that a species can possibly tolerate and use in the absence of competitors and predators, i. e free from any sort of interference from other species. Thus, fundamental niche is hypothetical.

Where as, realized niche is the actual smaller hypervolume which a species occupies under interference and predation from the other species. Because of interspecific interactions, the realized niche of a species is often smaller then fundamental niche.