Niche n. : A cavity, hollow, or recess, generally within the thickness of a wall, for a statue, bust, or other erect ornament. hence, any similar position, literal or figurative.

Example:
How can an extinction open up a Niche for a new species to occupy?

Taxonomy
Niche, free encyclopedia, Niche Technology, search, exedra, apse, relational, species, targetable, portion, subset, market sector, Technology Inc, law-enforcement, enforcement software, software company, Nurses, Improving Care.

Defination from the web:
niche, a term describing the relational position of an organism's species. Niche market, a focused, targetable portion (subset) of a market sector. ... Stem cell niche. NICHE (Nurses Improving Care for Healthsystem Elders) Program, an organization dedicated to creating a ...