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Encyclopedia > Allopatric speciation

Allopatric speciation, also known as geographic speciation, occurs when populations physically isolated by an extrinsic barrier evolve intrinsic (genetic) reproductive isolation such that if the barrier between the populations breaks down, individuals of the two populations can no longer interbreed. Although there is some debate about the frequency of other types of speciation (such as sympatric speciation and parapatric speciation), all evolutionary biologists agree that allopatry is a common way that new species arise. Speciation refers to the evolutionary process by which new biological species arise. ... Sympatry is one of three theoretical models for the phenomenon of speciation. ... Parapatric speciation is a form of speciation in which the evolution of reproductive isolating mechanisms occurs when a population enters a new niche or habitat within the range of the parent species. ...

The evolution of reproductive isolation is generally thought to be an incidental by-product of genetic divergence of other traits, particularly adaptive changes that evolve through natural selection in response to different environmental conditions in separate geographic areas. Ernst Mayr, an evolutionary biologist and famous proponent of allopatric speciation, hypothesized that adaptive genetic changes that accumulate between allopatric populations cause negative epistasis in hybrids, resulting in sterility or inviability. Natural selection is the metaphor chosen by Charles Darwin in 1859 to describe what he proposed to be the major force driving the evolution of new species and of those organismic attributes that allow life forms to negotiate their normal environments better than other environments (see Evolution, Adaptation). ... An example of epistastis would be sweet peas. ...

Allopatric speciation may occur when a species is subdivided into two large populations (vicariant or dichopatric speciation) or when a small number of individuals colonize a novel habitat on the periphery of a species' geographic range (peripatric speciation). Because natural selection is a powerful evolutionary force in large populations, adaptive evolution likely causes the genetic changes that results in reproductive isolation in vicariant speciation. In peripatric specation, however, the genetic changes that are thought to occur within the peripheral isolate are more controversial. Proponents of peripatric speciation contend that small population size in the peripheral isolate allows genetic drift, which can be a more powerful force than natural selection in small populations, to deconstruct complex genotypes, allowing the creation of novel gene combinations. Peripatric speciation (also known as Parapatry) is a type of speciation in the theory of natural selection. ... Species with a small population size are subject to a higher chance of extinction because their small population size makes them more vulnerable to genetic drift, resulting in stochastic variation in their gene pool, their demography and their environment. ... Genetic drift is a contributing factor in biological evolution, in which traits which do not affect reproductive fitness change in a population over time. ... The genotype is the specific genetic makeup (the specific genome) of an individual, usually in the form of DNA. It codes for the phenotype of that individual. ...

Speciation guide (edit)
Basic concepts: species | chronospecies | speciation
Modes of speciation: allopatric | parapatric | sympatric | polyploidy
Auxiliary mechanisms: sexual selection | punctuated equilibrium
Intermediate stages: hybrid | Haldane's rule

  Results from FactBites:
Speciation - Wikipedia, the free encyclopedia (718 words)
There are three main ideas concerning the emergence of new species (Modes of Speciation), each based on the degree to which populations undergoing this process are geographically isolated from one another (allopatric speciation, sympatric speciation, parapatric speciation).
During allopatric speciation, a population splits into two geographically isolated allopatric populations (for example, by habitat fragmentation or emigration).
New species have been created by domesticated animal husbandry, but the initial dates and exact methods of the initiation of such species are not clear.
  More results at FactBites »



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