Ecological speciation and its Types- Allopatric and Sympatric speciation

1. Ecological speciation
Dr. Emasushan Minj
Assistant Professor
Department of Botany

2. Introduction
• Ecological speciation is the process by which ecologically based
divergent selection between different environments leads to the
creation of reproductive barriers between populations.
• Natural selection is inherently involved in the process of speciation-
"under ecological speciation, populations in different environments,
or populations exploiting different resources, experience contrasting
natural selection pressures on the traits that directly or indirectly
bring about the evolution of reproductive isolation".
• Evidence for the role ecology plays in the process of speciation
exists.
• Studies of populations bear ecologically-linked speciation arising as
a by-product, along numerous studies of parallel speciation which
proves speciation's occurrence in nature.

3. • The key difference between ecological speciation and other kinds of
speciation is that it is triggered by divergent natural selection among
different habitats- as opposed to other kinds of speciation processes,
like random genetic drift, the fixation of incompatible mutations in
populations experiencing similar selective pressures, or various forms
of sexual selection not involving selection on ecologically relevant traits.
• Ecological speciation can occur either in allopatry, sympatry,
or parapatry.

4. Parallel speciation
• It is where "greater reproductive isolation repeatedly evolves between
independent populations adapting to contrasting environments than
between independent populations adapting to similar environments".
• It is a special form of parallel evolution in which traits that determine
reproductive isolation evolve repeatedly in independent, closely related
populations as a by-product of adaptation to different environments.

5. Types of Speciation
• Speciation is the method of formation of new species. A species can be defined as
one or more populations of interbreeding organisms that are reproductively isolated
in nature from all other organisms. As natural selection adapts populations
occupying different environments, they will diverge into races, subspecies, and
finally separate species. When populations no longer interbreed, they are thought to
be separate species.
▫ Type 1. Allopatric Speciation
▫ Type 2. Sympatric Speciation

6. Type 1. Allopatric Speciation:
• Allopatric speciation is the evolution of species in a population that occupy
different geographical areas.
• Geographic isolation is often the first step in allopatric speciation.
• Other isolating mechanism may also operate that further restrict
reproduction between populations.
• An example of allopatric speciation is the Darwin’s finches.
• The finches varied from each other mainly in shape and size of beak and
color of the feathers or plumage.
• According to Darwin, the species in the South American mainland were the
original species from which different forms migrated to different islands of
the Galapagos and became adapted to the environmental conditions of
these islands. The adapted forms eventually became the new species.
• In the case of the finches, geographical isolation led to the development of
reproductive isolation and thereby to the origin of new species.

8. Type 2. Sympatric Speciation:
• Speciation within a population that occupies the same geographic
environment by either ecological isolation (differing habitats) or by
chromosomal aberrations as seen in plants is known as sympatric
speciation.
• Sympatric speciation happens when members of a population develop
genetic differences that prevent them from reproducing with the parent
type.

9. Thank you