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Difference Between Bottleneck Effect and Founder Effect

A bottleneck effect is when there is a very noticeable reduction in population size for a minimum of one generation time. A founder effect is when a few individuals move to a new region and start a new colony of limited genetic variation.

What is Bottleneck Effect?

Definition:

A bottleneck effect is when there is a marked decrease in the size of a particular population for at least one generation time.

Causes:

Many different factors can be responsible for triggering changes leading to a bottleneck effect. Habitat destruction, overexploitation such as overhunting of a species, or some random environmental disaster can all cause a bottleneck to occur.

Consequences:

The consequences of a population bottleneck are that the variation in the population’s genome drops drastically. This means genetic drift is more likely to take place and populations can change quite dramatically in terms of genetic variation and which alleles are present. This decrease in genetic variation could even lead to species extinction, in extreme cases.

Examples:

Hunting by people is believed to have initiated a bottleneck effect in the Northern elephant seal population, and thus today, even though the population has grown, the genome still shows the impact of historical overhunting. The limited genetic variation is still present because only a few individuals were left to breed. Bison in North America are also an example of a bottleneck; the population was severely overhunted such that today the genetic variation is low and all based on the genes of the Bison from North Dakota.

What is Founder Effect?

Definition:

A founder effect is really when a few individuals from a population start a new colony, usually in a new location, such that there is minimal genetic variation in the new population.

Causes:

One of the main causes of the founder effect is migration, and in animals, it is often due to a few individuals, representing a non-random sample of genetic information, arriving on an island. 

Consequences:

The founder effect is thought to lead to speciation in some cases, particularly where populations are kept separate from the original population, such as in the case of islands. This occurs because only the genetic information from the few founder individuals is present in the new population, and often the environmental conditions are different in the new place compared with the conditions where the original population is. These new environmental factors, mean that the population then adapts and evolves, often becoming different from the original population.

Examples:

An example of the founder effect is illustrated by the desert bighorn sheep found on Tiburon Island. There were originally only about 20 founders on the island but now the population has grown to over 600 sheep, but the genetic variation is still low due to the founder effect. A further example is Darwin’s finches, where initially, a few individuals of a mainland Geospiza finch arrived on the islands. Subsequently, adaptive radiation occurred in time with several species of finches arising due to adaptations to different conditions on the Galapagos Islands.

Difference between Bottleneck effect and Founder effect?

Definition

A bottleneck effect is when there is a decline in the size of a particular population for at least one generation time. A founder effect is when a small number of individuals from the original population start a new colony, usually in a new location.

Causes

Many factors can result in a bottleneck effect, including natural disasters, overhunting or habitat destruction. A founder effect is caused by the migration of a small number of individuals from a population and colonization in a new location.

Random or non-random sampling of genes

A bottleneck effect occurs by chance and results in a random sampling of genes. A founder effect occurs through movement of specific individuals and involves a non-random sampling of genes.

Involves isolation from the original population

A bottleneck effect occurs in the original population and thus does not involve isolation from this population. A founder effect involves isolation from the original population.

Impacts the original population

Due to how it occurs, the bottleneck does always affect the original population in a big way. The process of the founder effect means that it does not affect the original population because individuals leave the population.

Examples

The Northern elephant seal and the Bison of North America are examples of the bottleneck effect. The Galapagos finches and desert bighorn sheep of Tiburon Island are both examples of the founder effect.

Table comparing Bottleneck effect and Founder effect

Summary of Bottleneck effect Vs. Founder effect

  • A bottleneck and a founder effect cause genetic variation to decrease due to genetic drift.
  • A bottleneck effect impacts the original population and is a random sampling of the genes.
  • A founder effect does not impact the original population since a few individuals leave and colonize a new area.

Dr. Rae Osborn

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References :


[0]Hedrick, P. W., G. A. Gutierrez‐Espeleta, and R. N. Lee. "Founder effect in an island population of bighorn sheep." Molecular Ecology 10.4 (2001): 851-857.

[1]Nei, Masatoshi, Takeo Maruyama, and Ranajit Chakraborty. "The bottleneck effect and genetic variability in populations." Evolution 29.1 (1975): 1-10.

[2]University of California at Berkeley. . "Bottlenecks and founder effects". University of California at Berkeley, 2020, https://evolution.berkeley.edu/evolibrary/article/bottlenecks_01

[3]Image credit: https://commons.wikimedia.org/wiki/File:Bottleneck_effect.jpg

[4]Image credit: https://commons.wikimedia.org/wiki/File:Founder_effect_with_drift.jpg

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