Practice question

Experimental removal of a competitor reveals whether biotic interactions restrict a species’ observed distribution. If a barnacle expands into additional intertidal space after its competitor is removed, the newly occupied zone was environmentally tolerable but previously inaccessible because of competition. That broader potential range belongs to the fundamental niche, whereas the restricted distribution observed with the competitor present is the realized niche. Thus the realized niche was smaller than the fundamental niche. Connell’s classic work on Scottish intertidal barnacles showed that Chthamalus could survive lower on the shore when Balanus was removed, but competition normally confined it to the upper zone. The experiment separates abiotic limitation from competitive exclusion: upper limits may be set by desiccation, while lower limits can be set by another species. Fundamental and realized niches are therefore not just mapped locations; they describe potential persistence versus actual occupancy under biotic conditions. Competitor removal does not imply mutualism, nor does it make the two niche concepts equal; it exposes the hidden portion of potential niche space.