Have you ever wondered what happens when a group of animals or plants are separated from their families? That's what we call allopatric speciation! It's when a group of the same species is separated by a physical barrier, like a river or a mountain, and over time they evolve into a new species. This process is also known as geographic speciation. There are different types of allopatric speciation, but the most common one is when a group of animals or plants are separated by a physical barrier and over time, they evolve into a new species. Allopatric speciation is different from sympatric speciation because sympatric speciation happens when a group of animals or plants evolve into a new species without being separated physically. Examples of allopatric speciation include the Galapagos finches, who evolved into different species when they landed on different islands, and the elephants in Africa, who evolved into two different species due to geographic isolation. So, next time you see a group of animals or plants separated by a physical barrier, remember that their way to becoming a new species through allopatric speciation!

How Does Allopatric Speciation Occur?

Let's delve deeper into allopatric speciation.

Allopatric Speciation Requires Geographical Isolation

When animals or plants live in the same area, they have a lot in common. Their genes are pretty similar, and they can mate with each other. But when they get separated by things like mountains, oceans, or rivers, they can't mate anymore. This is called geographic isolation. Because the animals or plants can't mate anymore, their genes start to change. The differences in their environment, like weather, food, and predators, make their genes change even more. This means that over time, they become a completely new species! As the groups of animals or plants become more and more different, they can't mate with each other anymore, even if they live in the same area. This is called reproductive isolation. This means that they have become so different that they can't make babies together. So, the next time you see two groups of animals or plants that look different, remember that they might have once been the same species, but over time they evolved into something new because of geographic isolation!

Figure 1 shows an experiment demonstrating allopatric speciation in the fruit fly (Drosophila pseudoobscura). A single population was split into two: one group was fed starch-based food, while the other group was fed maltose-based food. Over time, the populations diverged. When the two groups were mixed, they no longer mated with the other group members.

‍

We have mentioned that geographical changes, such as the formation of valleys and rivers, can cause allopatric speciation. But human activities such as the construction of roads and highways and environmental pollution can displace species from their habitat and cause allopatric speciation.

What Are the Types of Allopatric Speciation?

There are two different types of allopatric speciation: peripatric and vicariant. Let's talk about peripatric speciation first.

Peripatric speciation happens when a small group of animals or plants gets separated from the main group and starts their own population in a new area. This new population will have different genes from the main population because they were chosen randomly, not because they were better. Because the new population is so far away from the main population, they can't mate anymore. This means that the new population will keep evolving on its own, and eventually, it will become a new species! So, remember that peripatric speciation happens when a small group of animals or plants start their own population somewhere else and evolve into a new species because they can't mate with the main population anymore..

‍

A storm causes a few members of a population to be blown away. They become isolated on a different island, establishing a new population. This happens indiscriminately; individuals and their alleles that are transported- are selected at random. Over time, the new island population will be genetically different from the original population. This may lead to the formation of a new species. Vicariant speciation—also known as dumbbell speciation—occurs when a physical barrier, like a river or a valley, splits a population of a single species into two or more reproductively isolated groups. This process is illustrated in Figure 3 below.

‍

What are Examples of Allopatric Speciation?

This section will discuss two examples of allopatric speciation: the Galapagos finches and the squirrels on the Grand Canyon.

Darwin’s Finches on the Galapagos Islands

The Galapagos Islands are famous for their diverse range of finches. Despite their similar size and color, each species of finch has a unique beak shape that helps them survive in their environment. Some have broad, blunt beaks that are perfect for cracking nuts and seeds, while others have long, pointed beaks that allow them to snatch insects more easily. Interestingly, all of the finch species on the Galapagos Islands can be traced back to a single parent species that arrived on the islands millions of years ago. As the parent species spread from one island to the next, they became geographically isolated from each other. Over time, the different populations adapted to their new environments and evolved into distinct species with unique characteristics. This process of evolution through geographic isolation is known as allopatric speciation. By becoming isolated from each other, the different populations of finches were able to evolve independently and adapt to their specific environments. Eventually, they became so different from each other that they could no longer interbreed and became separate species. The finches of the Galapagos Islands are an excellent example of how evolution works in the real world. By adapting to their environment through natural selection, these finches were able to develop unique traits that allowed them to survive and thrive on the islands.

‍

Squirrels on the Grand Canyon

When Arizona's Grand Canyon formed approximately 10,000 years ago, a single population of squirrels became geographically separated, with the Grand Canyon acting as a physical barrier that prevented the isolated groups from interbreeding. This separation caused the gene flow from the Abert's squirrel to be cut off, and the Kaibab squirrel (Sciurus aberti kaibabensis) began to evolve on its own. Eventually, the squirrel population diverged into two subspecies: the Kaibab squirrel inhabiting the north rim and the Abert squirrel (S. a. aberti) inhabiting the south rim. These two subspecies can be differentiated based on features like the coloration of their belly and forelimbs. While they have not fully diverged into new species, they are well on their way; subspecies are considered to be in the first stage of speciation because the individuals rarely interbreed, and when they do, they often produce sterile male offspring.

‍

Can Allopatric Speciation Occur in Plants?

While allopatric speciation is more commonly observed in animals, it can also occur in plants. However, most plants undergo a different type of speciation called sympatric speciation, where two groups of the same species live in the same geographical area but no longer interbreed due to the formation of reproductive barriers.

That being said, there are some instances where allopatric speciation has occurred in plants. One such example is the Hawaiian "silversword alliance". The various species that comprise this alliance evolved from a single ancestral species that arrived on the Hawaiian Islands via long-distance dispersal. As the population of the ancestral species spread across the islands, they became geographically isolated from each other and adapted to their specific environments, giving rise to different species. Selective pressures such as drought, temperature, and soil conditions acted on the isolated populations, leading to the evolution of different morphological characteristics and reproductive strategies in each species. As a result, the various species in the silversword alliance have different leaf shapes, sizes, and colors, and they also differ in their flowering times and pollination strategies. Overall, the Hawaiian silversword alliance is an example of how allopatric speciation can occur in plants, given the right conditions and selective pressures.

Example of Allopatric Speciation in Plants: the Hawaiian "Silversword Alliance"

The Hawaiian silverswords are a group of various plant species that are genetically similar despite looking quite different from each other. Evidence shows that all the silverswords of Hawaii descended from the tarweed (Carlquistia muirii) from North America, which arrived on the islands via long-distance dispersal. Like the finches on the Galapagos, the tarweed occupied the uninhabited and geologically diverse islands of Hawaii, spreading into different ecological niches and forming different adaptations that ultimately led to the formation of the different species of Hawaiian silverswords.

Hawaii's diverse geological conditions, including variations in elevation, rainfall, and soil conditions, have led to the development of many unique life forms, with the silverswords being just one of the 1,100 plant species that are endemic to the Hawaiian islands. The silverswords range from low bushes to tall shrubs and have different leaf shapes, sizes, and colors, as well as different flowering times and pollination strategies.

The Hawaiian silverswords are an excellent example of how adaptive radiation can occur in plants, leading to the formation of different species from a common ancestor. The silverswords' evolution is a result of the unique geological and ecological conditions present in Hawaii, which have allowed for the diversification of life forms and the development of numerous unique species.

‍

Allopatric vs. Sympatric Speciation: What is the Difference?

Allopatric speciation is a type of speciation that occurs when populations of a species become isolated due to geographic separation. This separation leads to a lack of gene flow between the populations, causing the allele frequencies to change independently. Over time, the differences between the populations become more pronounced, eventually leading to the formation of new species.

There are two types of allopatric speciation: peripatric speciation and vicariant speciation. Peripatric speciation occurs when a small group of individuals becomes isolated from the main population and establishes a new population in a peripheral location. Vicariant speciation occurs when a physical barrier, such as a river or valley, splits a single population into two or more groups that become reproductively isolated.

One key difference between allopatric and sympatric speciation is that allopatric speciation requires geographic isolation, whereas sympatric speciation occurs without geographic separation. Instead, sympatric speciation occurs when members of a population evolve reproductive isolation mechanisms, such as polyploidy, sexual selection, or habitat differentiation, that prevent gene flow even when they still inhabit the same area.

Overall, understanding the different types of speciation and the mechanisms that drive them is crucial for understanding the diversity of life on Earth and how it has evolved over time.

Allopatric Speciation

What is allopatric speciation?

Allopatric speciation is a type of speciation that occurs when populations are split due to geographic isolation. 

What are types of allopatric speciation? 

There are two types of allopatric speciation: peripatric speciation and vicariant speciation. Peripatric speciation occurs when members of a population become isolated on a location peripheral to the main population and establish a new population. Vicariant speciation occurs when a physical barrier, like a river or a valley, splits a population of a single species into two or more groups that are reproductively isolated. 

What is the difference between allopatric and sympatric speciation?

An important difference between allopatric and sympatric speciation is that allopatric speciation involves geographic isolation while sympatric speciation does not. In sympatric speciation, members of a population evolve reproductive isolation and diverge into new species even when they still inhabit the same area. 

What is the first step in allopatric speciation?

The first step in allopatric speciation is the geographic separation of populations of the same species.

What are types of allopatric speciation? 

There are two types of allopatric speciation: peripatric speciation and vicariant speciation. Peripatric speciation occurs when members of a population become isolated on a location peripheral to the main population and establish a new population. Vicariant speciation occurs when a physical barrier, like a river or a valley, splits a population of a single species into two or more groups that are reproductively isolated.

‍