Practice question

Ecological compression is an immediate or short-term contraction of a species’ realized niche in response to competitors. Individuals alter behavior, habitat use, or diet within their existing capacities, and the change can reverse when the competitor disappears. Because no heritable evolutionary change is required, the process operates over ecological timescales—within lifetimes or across a few population cycles. Character displacement, in contrast, involves natural selection and genetic divergence over evolutionary time. Geological timescales concern large Earth-history processes, while “genetic timescale” is not a standard alternative category here. Compression can be detected by comparing resource use in sympatry and allopatry or before and after competitor removal. For example, a bird may forage only in upper canopy layers when a competitor occupies lower layers, then broaden its foraging range after removal. The fundamental niche remains the potential range; the realized niche is temporarily narrowed. Persistent compression can create selection favoring specialization, potentially leading eventually to character displacement, but the two mechanisms should not be conflated.