Realized niche width
Realized niche width, is a phrase relating to ecology, is defined by the actual space that an organism inhabits and the resources it can access as a result of limiting pressures from other species (e.g. superior competitors). Experiment. The phenomenon was documented by the ecologist Joseph Connell in his study of species overlap between barnacles on intertidal rocks. He observed that Chthamalus stellatus and Balanus balanoides inhabited the upper and lower strata of intertidal rocks respectively, but only "Chthamalus" barnacles could survive both the upper and lower strata without desiccation. The removal of "Balanus" barnacles from the  lower strata, resulted in the "Chthamalus" barnacles occupying its fundamental niche (both upper and lower strata) which is much larger than its realized niche in the upper strata. Fundamental niche width "vs." realized niche width. The "fundamental niche width" of an organism refers to the theoretical range of conditions that it could inhabit and successfully survive and reproduce without interspecific interactions as well as other limiting biotic and abiotic factors like appropriate food sources and a suitable climate. The fundamental niche width often differs from the "realized niche width". (the areas that a species actually inhabits and persists). This is  due to interspecific competition with other species within their ecosystem and other biotic and abiotic limiting factors. A species' realized niche is usually much narrower than its "fundamental niche width" as it is forced to adjust its niche around the superior competing species. The physical area where a species lives, is its "habitat." The set of environmental features essential to that species' survival, is its "niche." (Ecology. Begon, Harper, Townsend)