A species is a group of organisms that can mate with one another to produce
fertile off-springs. If individuals cannot mate with each other then they are of different species.
Speciation is the process where a species diverges into two or more descendant
species. It is the evolutionary process by which new biological species arise.
Interruption in Gene flow as time passes, DNA starts becoming more and more
different means new species are evolved.
Populations of species that live without interbreeding, over time, enough
differences in characteristics arise that they can no longer interbreed.
Reasons for speciation:
Apart from this, population bottleneck or genetic diversity also results in speciation which is also caused by either natural (earthquakes, floods, fire, disease, or droughts) events or anthropogenic causes.
Population bottleneck and genetic diversity
A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population caused by natural or anthropogenic causes. Such events can reduce the variation in the gene pool of a population. As a consequence population size reductions and the loss of genetic variation, the robustness/fitness of the population is reduced along with its ability to adapt to severe conditions of the environment (climate change, or any other calamities) is also reduced.
Due to the loss of genetic variation, the new population can become genetically distinct from the original population, which has led to the hypothesis that population bottlenecks can
lead to the evolution of new species.
Due to the smaller population size after a bottleneck event, the chances of inbreeding increase, and Genetic homogeneity increases leading to the potential for inbreeding depression.
Types of Speciation:
Allopatric Speciation
- This occurs in populations initially isolated geographically(large river, ocean, mountains, continent drift).
- Selection and drift act independently on populations isolated from the rest of their species (reproductive isolation).
- Very rapid changes in the appearance and behavior of organisms (due to natural selection/adaptation).
- Can occur in a relatively short time when one species gives rise to many species in response to the creation of new habitat or another ecological opportunity
- Separation may eventually produce organisms that cannot interbreed
Peripatric Speciation
- Similar to allopatric speciation, peripatric speciation involves populations being geographically separated and prevented from exchanging genes.
- It differs from the allopatric speciation in the way that the population separating from the main population involves a smaller unit(from the periphery).
- Peripatric is a subgroup of allopatric speciation.
- Unique characteristics of the small groups are passed on to future generations, making those traits more common among that group and distinguishing them from the other.
- Genetic drift (founder effect) plays a major role in this speciation
Parapatric Speciation
- This occurs due to the reproductive barrier, no geographic barrier.
- This specification happens in a continuous population where there is no extensive barrier to gene flow.
- It often happens when part of an environment has been polluted and that changes its biological characteristics like the flowering period.
- The population does not mate randomly, individuals mate with neighbors
Sympatric Speciation
When many organisms have more than two sets of homologous chromosomes are called polyploidy.
The speciation which occurs when the individuals in the same habitat are
reproductively isolated from each other is referred to as sympatric speciation. It mostly occurs through polyploidy.
When an offspring inherits more than the normal chromosome number in the population, this offspring is incapable of reproducing with individuals who contain the normal chromosome number of the population.
A new species can arise if a genetic change produces a reproductive barrier
between mutants and the parent population.
There is genetic barrier that leads to speciation.
How can one species become two separate species living in the same area?
- Due to mutation
- Change in allele frequency
- Behavior change
- Reproductive isolation
- Preference changes
- Seasonal reproduction
