Speciation | Species | Geographical Isolation

Isolation and Speciation 

 Key Concepts

• Natural selection
• Speciation
• Species
• Geographical isolation
• Separation
• Adaptation
• Division

Introduction

We know that nature also has its process of selection. All living organisms compete for food, water, sunlight, space and other resources. The organisms that are best able to obtain food and escape predation survive and reproduce.  

Natural selection is the process by which individuals with traits that better suit the environment are more likely to survive longer and reproduce more successfully than those without these traits. 

 Inherited traits that increase an organism’s chance of surviving and reproducing in a particular environment are called adaptations. Adaptations only spread through a population in future generations if natural selection favors them. 

Explanation

Genetic variation: 

Genetic differences are responsible for the variation between species and between members of the same population. The genetic variation of a particular population measures how much the individuals in that population differ genetically. In a population that has high genetic variation, the members have different alleles or forms of their genes. Due to this, the population will have a large variety of traits. In contrast, the individuals in a population that has low genetic variation have many of the identical alleles. Therefore, that population has a small variety of traits. Genetic variation is essential for the survival of a species. 

Populations having a low genetic variation are less likely to adapt to changes in their environment than populations with a high genetic variation. 

Environmental factors: 

Environmental factors are the conditions in that environment that affect the organisms living there. Different types of environments have different environmental factors. For example, desert organisms should be able to survive in an area that receives little water. And organisms that live near the coral reefs need to be able to survive in saltwater. Also, organisms living near a coral reef have different food sources and different predators than organisms in deserts do. Thus, we can say that certain traits are better in specific environments. 

Speciation: 

Speciation is the formation of a new species from a pre-existing species due to evolution. At times, drastic changes that can lead to the formation of a new species take place.  

It occurs when a group of organisms within a species separates from other members of its population and develops its own unique characteristics. 

The two populations differ so significantly that they can no longer mate with each other. The new population may now be considered as a new species. The formation of a new species occurs at a slow pace and through natural selection, in which the individuals that are best adapted survive and the ones that are least adapted die. 

Species: 

A species is a group of organisms that can mate with each other to produce fertile offspring. Organisms in a species generally look similar to each other. 

How are new species formed? 

A new species may form after a group of organisms becomes separated from the original population. This group now forms a new population. Over the course of time, the two populations adapt to their environments. Eventually, the populations become so different that they cannot mate with each other anymore. 

As a result of these, new species are formed, and this process is known as speciation. We have studied about Darwin and his investigations on finches of the Galapagos Islands. The different species of finches are formed as a result of separation. Let us understand how the speciation in finches took place. 

We know that all these finches originated from the same ancestral finch from the mainland of Ecuador but later got separated and adapted to their particular environments. In this case, the ocean present between the Galapagos Islands was the main reason for the separation of these finches. We can also say that geographical isolation caused the formation of new species in this case. 

Geographical isolation: 

Geographical isolation refers to the separation of members of a population by a physical barrier, such as a mountain range, rivers,  volcano, oceans, glacier or a newly formed lake. These physical barriers cause the members of a species to separate into two groups or populations. The movement of the Earth’s continental and oceanic plates can also affect the distribution of organisms.  

These species then evolve separately and inherit characters that favor their survival in their particular environment. As a result, the original species are divided into two distinct species that cannot interbreed. 

Factors contributing to speciation: 

Different factors can contribute to speciation, one of which is isolation. 

Speciation can also occur as a result of a competition to find mates. The females of many species of birds prefer to mate with males that have certain types of colorful feathers.  

Sometimes, similar-looking organisms do not mate with each other as their reproductive cycles or mating periods occur at different periods of time. This change in the time of the reproductive cycle could be a result of an adaptation that was inherited through generations. 

For example, the leopard frog and pickerel frog are similar species and probably have a common ancestor but do not mate with each other as they have different mating seasons. 

Leopard frog and pickerel frog are similar species but do not search for mates at the same time. 

Speciation can also occur when similar species exhibit different courtship behavior. This can include differences in mating songs or mating rituals. For example, the eastern and western meadowlark are similar species, but they have different mating songs. As a result, these two species do not breed with each other. This could be due to speciation. 

Western Meadowlark and Eastern Meadowlark are similar birds, but they will not interbreed because they use different mating songs to attract mates. 

Steps involved in speciation. 

We can say that the formation of new species takes place in three steps: 

1. Separation 

2. Adaptation 

3. Division 

Separation: 

Species of a population gets separated as a result of geographical barriers, behavioral or environmental barriers. Separation is the first step of speciation. It prevents members of the same species from interacting with each other in future generations if natural selection favors them. 

Adaptation: 

After two groups have separated, populations constantly undergo natural selection. Over many generations, the groups may acquire different sets of traits. If the environmental conditions for each group are different, the groups’ adaptations will also differ.  

For example, consider a population of birds that have separated into two groups after living on two different islands. The birds living on the island, which has bigger, tougher seeds, will probably have different adaptations for eating than the birds that are living on the island that has small, soft seeds will. 

Division: 

Over many generations, the separated groups of the population become very different from each other. Now, even if we remove the geographical barrier, the two groups may not be able to breed anymore. As a result, the two groups are no longer considered as the same species. 

Summary

• Natural selection is the process by which individuals with traits that better suit the environment are more likely to survive longer and reproduce more successfully than those individuals without these traits.
• Speciation is the formation of a new species from a pre-existing species due to evolution.
• It happens when a group within a species separates from other members of its species
  and develops its own unique characteristics.
• A species is a group of organisms that can mate with each other to produce fertile offspring A new species may form after a group becomes separated from the original population.
• Over the course of time, the two populations adapt to their environments.
• Eventually, the populations become so different that they cannot mate with each other
  anymore.
• Separation or isolation refers to the separation of members of a population by a physical
  barrier, such as a mountain range, rivers, volcano, oceans, glacier or a newly formed lake.
• Adaptations refer to the changes in an organism occurring as a result of changes in its
  environment.
• Division is when two groups of a species show so much variation that even after the removal of the barrier, they cannot interbreed.