Frequency-dependent selection
Frequency-dependent selection is an evolutionary process by which the fitness of a phenotype or genotype depends on the phenotype or genotype composition of a given population.In positive frequency-dependent selection, the fitness of a phenotype or genotype increases as it becomes more common.
In negative frequency-dependent selection, the fitness of a phenotype or genotype decreases as it becomes more common. This is an example of balancing selection.
More generally, frequency-dependent selection includes when biological interactions make an individual's fitness depend on the frequencies of other phenotypes or genotypes in the population.
Anvil stone, where a thrush has broken open shells of polymorphic Cepaea snails; its selection of morphs may be frequency-dependent.
Harmless scarlet kingsnake mimics the coral snake, but its pattern varies less where the coral snake is rare.
Venomous coral snake's warning coloration can benefit harmless mimics, depending on their relative frequency.
Müllerian mimetic species of Heliconius from South America
Fitness is a quantitative representation of individual reproductive success. It is also equal to the average contribution to the gene pool of the next generation, made by the same individuals of the specified genotype or phenotype. Fitness can be defined either with respect to a genotype or to a phenotype in a given environment or time. The fitness of a genotype is manifested through its phenotype, which is also affected by the developmental environment. The fitness of a given phenotype can also be different in different selective environments.
Herbert Spencer
Image: Selective sweep, frequency vs time