Speciation is the process of dividing an ancestral species into two descendant species, reproductively isolated from each other.
In summary, speciation is the process of formation of new species of living beings.
Reproductive isolation is the determining factor for the origin of a new species.
Remember, the species concept refers to a group of populations that interbreed and are reproductively isolated from individuals of other species.
Speciation and the current diversity of living beings, according to their adaptation to the environment and ability to transmit the characteristics to their descendants, can be explained by Natural selection.
There are three main models of speciation: allopatric, parapatric and sympatric.
Allopatric Speciation
It is based on the formation of new species in geographically isolated populations.
With the geographical isolation between two populations, crosses between their members no longer occur. Thus, gene flow is interrupted, so that some new feature in one population is not shared with the other. Over time, the tendency is that the particular adaptation of each one leads to reproductive isolation.
Geographic isolation among populations of a species can occur through vicariance or dispersal events.
Therefore, there are two main types of allopatric speciation, based on the form of geographic isolation:
Vicarious Speciation
It occurs when an ancestral population is distributed over two or more areas and an effective barrier arises between isolated subpopulations.
Vicarious effect is called the process that divides the geographic area of a population into discontinuous parts, due to the formation of a physical barrier. Example: emergence of mountain ranges.
This physical barrier prevents the dispersal of individuals and makes it impossible for them to cross. With the lack of gene flow between two populations, they tend to become more and more different. Over time, the result is speciation.
Peripatric Speciation
Peripatric (from the Greek peri, around, around).
Also called the “Founder Effect”.
It occurs when, through dispersion, a peripheral colony is formed from the original population and, after several generations, reproductive isolation arises.
In this type of speciation, individuals disperse through a preexisting barrier and settle in an uninhabited area. The dispersed population can undergo mutations, which differentiate it from the ancestral population.
Parapatric Speciation
It takes place without geographic isolation. Populations of the same species are in a single area, with different adjacent habitats.
However, even if there is no physical barrier to gene flow, the population does not cross randomly.
In general, it occurs when the species spreads over a large area, with diverse environments.
Individuals are distributed over one or more adjacent areas with different niches and selective pressures. This situation leads each population to its local adaptation and consequently to become new species.
Sympatric Speciation
Sympatric speciation (syn, similar, together; patriae, place of birth) does not involve geographic isolation.
It occurs when two populations of the same species live in the same area, but there is no crossing between them, which leads to differences that result in speciation.
In this type of speciation, it is a biological barrier that prevents interbreeding.
In nature, sympatric speciation can be observed and explained through two mechanisms: disruptive selection and chromosomal alterations.
The most common way is by polyploidy (mutation), which represents an increase in the number of chromosomes. This mechanism occurs more in plants than in animals.
New species can arise abruptly as a result of chromosomal mutations.
