Disruptive selection

Illustration of disruptive selection showing the shift in population distribution.

Disruptive selection is a type of natural selection that simultaneously favors individuals at both extremes of the distribution. This form of selection can lead to a bimodal distribution of traits within a population, where two distinct phenotypes are favored over the intermediate phenotype.

Mechanism

Disruptive selection occurs when environmental conditions favor individuals at both extremes of a phenotypic range. This can happen in environments that are heterogeneous or where there are distinct niches that different phenotypes can exploit. For example, in a population of birds, if both very large and very small beaks are advantageous for accessing different types of food, individuals with intermediate beak sizes may be at a disadvantage.

Examples

One classic example of disruptive selection is seen in the Darwin's finches on the Galápagos Islands. In some species, finches with either very large or very small beaks have a selective advantage, as they can access different food sources more effectively than those with medium-sized beaks.

Another example can be found in the African seedcracker finch, where individuals with either very large or very small beaks are more successful in cracking different types of seeds, leading to a bimodal distribution of beak sizes.

Implications

Disruptive selection can lead to increased genetic diversity within a population and may even result in speciation if the two extreme phenotypes become reproductively isolated from each other. This form of selection is a key mechanism in the process of adaptive radiation, where a single ancestral species gives rise to a variety of new species adapted to different environments.

Related Pages

• Natural selection
• Speciation
• Adaptive radiation
• Darwin's finches
• Genetic diversity