standing variation

Rice AM & Pfennig DW 2007 Character displacement: in situ evolution of novel phenotypes or sorting of pre-existing variation? J Evol Biol 20:448-459.

• character displacement transpires when these pre-existing divergent phenotypes increase in frequency in sympatry relative to allopatry
• such sorting of pre-existing variation should unfold relatively rapidly
• species that express resource or mating polymorphism prior to interactions with heterospecifics may be more prone to undergo character displacement

• selection in allopatry may lead to the evolution of phenotypes that are pre-adapted for, and therefore differentially spread in response to, competition in sympatry
• this second route may make character displacement more likely to occur and may therefore be the more common route

• the possibility that sorting might function within species to promote character displacement is seldom considered