Where does character displacement collide?

In evolutionary ecology, character displacement is the pattern in which two closely related species that overlap geographically diverge more strongly in a competitive trait (bill size, body length, call frequency) where they co-occur than where each lives alone, because selection penalises the individuals most similar to a competitor. William Brown and Edward Wilson's 1956 Character Displacement named and documented the pattern across many taxa and argued it was a signature of competition shaping traits. The referent is the divergence of competing species in trait space to reduce niche overlap. It is the same rivalry-driven separation that economics frames as product differentiation, here written in heritable traits and species rather than prices and firms.[1]

Unit

The trait difference between competing species in sympatry versus allopatry

Recovery means

Not applicable

Measured by

Detected as exaggerated trait divergence where competitors co-occur, controlling for allopatric baselines

In organizational ecology, resource-partitioning theory describes how, as a market concentrates and a few generalists fight over its crowded centre, the periphery of the resource space opens up and specialist organisations proliferate there, so competitors survive by occupying separated niches rather than overlapping ones. Glenn Carroll's 1985 Concentration and Specialization: Dynamics of Niche Width in Populations of Organizations modelled these dynamics of niche width and showed why concentration among generalists can raise, not lower, the number of specialists. The referent is again competition-driven separation into distinct niches that permits coexistence, the same mechanism as character displacement and product differentiation, transposed from species and firms-on-a-line to whole populations of organisations dividing a resource space.[2]

Unit

The niche width and separation of organisations across a resource space

Recovery means

Not applicable

Measured by

Assessed by organisational niche width, market concentration, and the density of specialists on the periphery