The process by which new species of organisms evolve from existing species over time is known as speciation.
It is a key aspect of the theory of evolution and occurs when populations of a species become reproductively isolated from one another, meaning they can no longer interbreed and produce fertile offspring. Over time, these isolated populations may evolve differences in their genetic makeup, physical traits, behavior, or other characteristics.
If the differences become large enough, the populations can be considered distinct species. Geographic isolation, behavioral differences, and hybridization are all examples of mechanisms that can lead to speciation.
Types of speciation compared
Type of Speciation
Physical separation of a population
Formation of a geographical barrier (e.g. mountain range or ocean) divides a population, leading to isolation and subsequent evolution of two separate species.
Evolution within a shared geographical area
This type of speciation can occur due to mechanisms such as reproductive isolation, adaptation to different habitats within the same area, or genetic changes in small subpopulations.
Evolution along a gradient of geographic overlap
This type of speciation can occur when two populations are partially overlapping geographically, and reproductive isolation evolves along a gradient of geographical separation.
Evolution from a small, isolated subpopulation
This type of speciation occurs when a small subset of a population becomes geographically isolated, evolves separately, and eventually becomes a new species.
Evolution through changes in ploidy
This type of speciation occurs when an organism has multiple sets of chromosomes, leading to a reproductive barrier and the evolution of a new species. It is commonly observed in plants.
Can speciation of plants benefit humans?
By <a href=”//commons.wikimedia.org/w/index.php?title=User:Nathalyt912&action=edit&redlink=1″ class=”new” title=”User:Nathalyt912 (page does not exist)”>Nathaly Tamayo</a> – <span class=”int-own-work” lang=”en”>Own work</span>, CC BY-SA 4.0, Link
Speciation in plants can benefit humans in several ways:
- Plant speciation contributes to the overall diversity of life on Earth by producing a diverse range of species that can be used for food, medicine, and other products.
- Crop improvement: Speciation allows for the evolution of new crop varieties that are better suited to specific growing conditions, have higher yields, and are resistant to disease or pests. This has the potential to lead to more efficient and sustainable agriculture.
- Plant species that have evolved through speciation may have unique chemical compounds that can be used for medicinal purposes. Compounds from the Foxglove plant (Digitalis purpurea, for example) are used to treat heart conditions.
- Plant species may evolve through speciation to better adapt to changing conditions as the climate changes. This can aid in the preservation of biodiversity and ecosystem stability.
- Plants that have evolved through speciation are highly valued for their ornamental value and are used in landscaping and horticulture.
Why scientists believe the Abert’s and Kaibab squirrels are examples of speciation.
By <a rel=”nofollow” class=”external text” href=”https://www.flickr.com/people/42646706@N02″>Mike’s Birds</a> from Riverside, CA, US – <a rel=”nofollow” class=”external text” href=”https://www.flickr.com/photos/pazzani/4546426713/”>Abert’s Squirrel aka Tassel-eared Squirrel</a>, CC BY-SA 2.0, Link
The Abert’s squirrel and the Kaibab squirrel are often cited as examples of speciation because they are two distinct species that have evolved from a common ancestor but are now reproductively isolated from one another.
By <a href=”//commons.wikimedia.org/w/index.php?title=User:Azhikerdude&action=edit&redlink=1″ class=”new” title=”User:Azhikerdude (page does not exist)”>Azhikerdude</a> – <span class=”int-own-work” lang=”en”>Own work</span>, CC BY-SA 3.0, Link
The two species are similar in appearance and habitat, but they are found on opposite sides of the Grand Canyon in the United States and do not interbreed.
There are several factors that suggest that the Abert’s and Kaibab squirrels are the result of speciation.
Firstly, the Grand Canyon is a geographical barrier that has separated the two populations, leading to their physical isolation. Over time, each population has evolved in response to different environmental conditions, such as differences in food availability, predators, and climatic conditions.
Furthermore, genetic studies have revealed that the two species’ DNA differs, indicating that they evolved independently of one another. A study, for example, discovered that the two species have different alleles (versions of the same gene) at many loci (positions on the chromosome), implying that they evolved independently over a long period of time.
Overall, the Abert’s and Kaibab squirrels are good examples of speciation because they are two distinct species that evolved from a common ancestor but are now reproductively isolated from one another.
The geographical barrier of the Grand Canyon and genetic differences between the two species support the conclusion that they are the result of speciation.
Order of events in allopatric speciation
The order of events in allopatric speciation is as follows:
- Physical separation: A population of a species becomes physically separated, usually by the formation of a geographical barrier such as a mountain range, river, or ocean.
- Genetic differentiation: Over time, the separated populations experience different selective pressures and genetic drift, leading to the evolution of different traits and genetic differences between the populations.
- Reproductive isolation: As the populations continue to evolve and differentiate, they may develop reproductive barriers, such as differences in mating behaviors, songs, or physical adaptations, that prevent them from interbreeding and producing fertile offspring.
- Speciation: Once the populations have become reproductively isolated, they are considered separate species, and speciation has occurred.
It is important to note that allopatric speciation can take a long time and may involve multiple cycles of genetic differentiation, reproductive isolation, and speciation. The precise timeline will be determined by a variety of factors, including population size, genetic drift rate, and natural selection speed.
Factors that contribute to allopatric speciation
Allopatric speciation is influenced by a number of factors, including:
- Physical separation: Physical separation of a population, usually by the formation of a geographical barrier such as a mountain range, river, or ocean, is a key factor in allopatric speciation. This separation allows the populations to evolve independently, without interbreeding.
- Genetic drift: The smaller size of the separated populations increases the influence of genetic drift, which can lead to the evolution of different traits and genetic differences between the populations.
- Natural selection: The separated populations may experience different selective pressures, such as different climates, food sources, or predator populations. This can lead to the evolution of adaptations that are better suited to the local environment.
- Mutations: New mutations can arise in the separated populations and spread through the population if they provide a selective advantage.
- Sympatric factors: Sexual selection or differences in mating behavior, for example, can also contribute to reproductive isolation and speciation in allopatric populations.
What prevents speciation from occurring in sympatric populations?
Several factors can prevent speciation in sympatric populations, where two or more species share the same geographical range, including:
- Gene flow: Extensive gene flow between populations, implying significant interbreeding and genetic material exchange, can prevent populations from diverging and becoming distinct species.
- Hybridization: The interbreeding of two distinct species can blur genetic differences between populations, preventing speciation.
- Strong selective pressures: If strong selective pressures exist, such as resource competition or predation, it can limit population divergence and prevent speciation.
- Lack of genetic variation: If populations have limited genetic variation, natural selection’s ability to drive population divergence and prevent speciation is limited.
- Mutation rate: When the mutation rate is low, the availability of new genetic variations that could contribute to speciation is limited.
Speciation may occur in sympatric populations in certain circumstances, such as when the populations have different ecological niches or mating behaviors that allow for reproductive isolation to develop.
These situations, however, are less common in allopatric populations and may be hampered by the factors listed above.
Differences between adaptive radiation and other types of speciation?
Adaptive radiation is a process of rapid speciation where a single ancestral species gives rise to multiple descendant species in response to new ecological opportunities. The main difference between adaptive radiation and other forms of speciation, such as allopatric or sympatric speciation, is the rate and scope of speciation.
In adaptive radiation, multiple species can arise rapidly, within a relatively short period of time and geographical area, in response to new ecological opportunities.
For example, the evolution of Darwin’s finches on the Galapagos Islands is an example of adaptive radiation, where a single ancestral species of finch evolved into multiple species with distinct beak shapes and adaptations to different food sources.
Allopatric speciation, on the other hand, occurs when populations are physically separated by a geographical barrier, such as a mountain range, river, or ocean.
The populations then evolve independently, resulting in the formation of reproductive barriers and eventual speciation. Allopatric speciation can be time-consuming and may involve multiple cycles of genetic differentiation, reproductive isolation, and speciation.
Sympatric speciation occurs in populations that share the same geographical range and is usually caused by differences in mating behavior or ecological niches. In sympatric populations, the speciation process is slower and less common because gene flow and hybridization can blur genetic differences between populations and prevent speciation.
The main distinction between adaptive radiation and other forms of speciation is the rate and scope of speciation, with adaptive radiation being a rapid process that produces multiple species in response to new ecological opportunities.
Which type of natural selection is most likely to contribute to speciation?
All forms of natural selection can play a role in speciation, depending on the specific circumstances of the populations involved. However, divergent selection is most likely to play a key role in speciation.
Divergent selection occurs when populations are exposed to various selective pressures, such as different climates, food sources, or predator populations.
These differences can drive the evolution of adaptations better suited to the local environment, resulting in genetic differences between populations. These genetic differences can become so pronounced over time that the populations are unable to interbreed and separate into separate species.
Stabilizing selection, which occurs when populations are subjected to selection that favors intermediate traits and reduces genetic variation, can also contribute to speciation if it results in the evolution of reproductive isolation mechanisms.
For example, if two populations develop distinct mating behaviors or vocalizations that prevent interbreeding, this can result in reproductive isolation and, eventually, speciation.
Disruptive selection, which occurs when selection favors extreme traits over intermediate traits, can also contribute to speciation if it leads to the evolution of adaptations that are better suited to different habitats or ecological niches.
For example, if a bird population evolves into two distinct groups, one adapted to feeding in trees and the other to feeding on the ground, these adaptations can eventually lead to reproductive isolation and speciation.
Overall, the type of natural selection that is most likely to play a role in speciation will be determined by the populations involved’s specific selective pressures and evolutionary opportunities.
Why is genetic drift often a factor influencing speciation after a founder event?
Genetic drift is often a factor influencing speciation after a founder event because it can lead to rapid changes in the frequency of alleles (versions of a gene) in small populations. A founder event is the colonization of a new area by a small number of individuals, which can lead to the formation of a new, isolated population.
Chance events can have a large impact on the frequency of alleles in such a small population. For example, if a beneficial allele is present in the founding individuals, genetic drift can quickly fix it in the new population.
Similarly, if a harmful allele is present in the founders, it can become fixed in the new population.
The accumulation of genetic differences between the new and ancestral populations over time can lead to reproductive isolation and, eventually, divergence into a separate species. Genetic drift can also contribute to the loss of genetic variation in a new population, limiting natural selection’s ability to drive adaptation to the local environment.
How the timing of when fruit falls from a tree be important in sympatric speciation?
The timing of when fruit falls from a tree can be an important factor in sympatric speciation if it affects the behavior and interactions of different bird species that feed on the fruit.
Sympatric speciation occurs when populations of a species that share the same geographical range diverge into separate species.
If different bird species have different preferences for when fruit falls from a tree, this can lead to the evolution of adaptations that allow each species to specialize in a specific foraging time period. One bird species may prefer early-falling fruit, whereas another bird species may prefer late-falling fruit.
As a result of this specialization, the bird species may differ in other aspects of their behavior and biology, such as beak size or shape, vocalizations, or mating behaviors. These differences may result in the evolution of reproductive isolation mechanisms that prevent interbreeding between bird species over time.
In this way, the timing of when fruit falls from a tree can influence the evolution of adaptations that allow different bird species to specialize and eventually diverge into separate species, which can be an important factor in sympatric speciation.
This process shows how even minor differences in the timing of ecological events can drive speciation and species diversification.
How did the speciation of the galápagos finches happen?
The speciation of the Galápagos finches is one of the most famous examples of adaptive radiation, a process where a single ancestral species diverges into multiple species that occupy different ecological niches. The Galápagos finches are a group of 13-15 bird species found only on the Pacific Ocean’s Galápagos Islands.
The Galápagos finches are believed to have originated from a single ancestral species that arrived on the islands from South America. Over time, the ancestral species underwent adaptive radiation to fill the different ecological niches available on the islands, such as feeding on different types of seeds and fruits.
The availability of various food sources on the islands was a major factor in the speciation of the Galápagos finches. The Galápagos finches’ various beak shapes and sizes reflect the adaptations they have made to feed on the various types of seeds and fruits available on the islands.
For example, the ground finch (Geospiza fortis) has a large, heavy beak that is well-suited for cracking open hard seeds, while the warbler finch (Certhidea olivacea) has a thin, sharp beak that is well-suited for probing flowers for nectar.
In addition to food source differences, the Galápagos finches evolved behavioral differences, such as vocalizations, mating behaviors, and nesting habits. These differences may result in the evolution of reproductive isolation mechanisms that prevent interbreeding between finch species.