Practice question

Ecological compression is a short-term narrowing of resource use or habitat occupancy caused by the presence of competitors. Individuals shift behavior, foraging locations, or utilized resources within their existing phenotypic capacity, so the realized niche becomes narrower. The fundamental niche—the conditions under which the species could persist without the competitor—does not expand or contract merely because current competition changes. Compression can be reversed quickly if the competitor is removed, distinguishing it from character displacement, which involves heritable evolutionary divergence over generations. Increased overlap would intensify competition rather than describe the usual outcome; compression generally separates realized use or confines one species to a subset of available niche space. Examples include a bird feeding in fewer canopy layers when a competing species is present or a barnacle restricted to part of the intertidal zone. The magnitude of narrowing depends on competitive strength, resource availability, and behavioral flexibility. Reduced niche breadth is therefore the direct ecological signature, while long-term selection may subsequently transform repeated competitive pressure into evolutionary niche differentiation.