Practice question

A fundamental niche comprises the abiotic conditions and resources under which a species could maintain a population in the absence of restrictive biotic interactions. A realized niche is the portion actually occupied when competitors, consumers, pathogens, mutualists, and dispersal constraints operate. Competition commonly excludes a species from otherwise physiologically suitable environments, making the realized niche narrower than the fundamental niche. Connell’s barnacle experiments illustrate this: removing a dominant competitor allowed the subordinate species to occupy a broader intertidal range, revealing that competition had restricted its field distribution. Absence of competitors would permit expansion toward the fundamental niche rather than explain contraction. Predator absence and abundant resources may also broaden occupancy, though predators or mutualisms can sometimes produce more complex relationships. The realized niche is not invariably a strict subset in every conceptual framework because positive interactions can enable occupancy beyond conditions tolerated alone, but the classical competition example assumes restriction. The key principle is that potential tolerance sets the fundamental range, while actual biotic context filters which parts are realized in nature.