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Earth is home to approximately 8.7 million species spread across various biospheres. The immense diversity is responsible for the effective functioning of the planet. Biodiversity exists at all levels of biological organisation (from macromolecules within cells to biomes).
The rise and fall of the number of species is a phenomenon that is expected according to the Laws of Nature. The extinction and endangerment of different species has been occurring ever since the first species evolved on the planet.
Extinction, which earlier used to be a natural process, is now also heavily influenced by human actions.
| Table of Content |
Key Terms: Extinction, mass extiction, vertebrate species, habitats,
Definition of Extinction
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Extinction refers to the elimination of a species from the planet. It is a process of evolution that ends the genetic continuity of any given population. Extinction can be caused due to natural calamities, evolutionary changes, and more often, nowadays, due to human interference.
Read More:
| Important Topics | ||
|---|---|---|
| Ecology and Environment | Population | Acclimatization |
| Community (definition) | Marine biology | Pelagic zone |
There are certain species which have been extinct for millions of years, like dinosaurs or mastodons. In recent years, we have seen the extinction of several species, among which the most famous are the Dodo bird and Messenger Pigeons.
Types of Extinction
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Extinctions can be broadly categorized into two types:
- Mass extinction
- Pseudo extinction
Mass Extinction
When large numbers of species are collectively wiped out over a relatively short period of time in the geological time scale, it is termed as a mass extinction. Mass extinctions have occurred a few times over the past. It is assumed that the largest mass extinction took place around 250 million years ago, affecting approximately 90% of the global species at that time.
Top Five Mass Extinctions
- Ordovician-silurian Extinction (440 million years ago): Affected small marine organisms
- Devonian Extinction (365 million years ago): Affected many tropical marine species.
- Permian-triassic Extinction (250 million years ago): The largest mass extinction event in Earth's history; affected several species, including many vertebrates.
- Triassic-jurassic Extinction (210 million years ago): The extinction of other vertebrate species on land allowed dinosaurs to flourish.
- Cretaceous-tertiary Extinction (65 Million Years Ago)
Eath mass Extinction
Pseudo Extinction:
When the genetic heritage of an extinct species evolves and is continued by members of a daughter species, that phenomenon is termed as pseudo-extinction or phyletic extinction.
An example of pseudo-extinction is the evolution of birds as we know them from avian dinosaurs.
Morphology and Extinction
Read more: difference between environment and ecology
Causes of Extinction
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- Fragmentation of Habitat :
Loss of habitat is the leading cause of extinction among various species. The largest impact is felt through the destruction of tropical rainforests. Large habitats break into small fragments due to various human activities. Mammals and birds requiring large territories and certain animals with migratory habits are the one negatively affected by it, leading to population decline and ultimately causing extinction.
- Over- Exploitation of Species :
This is chiefly a human created cause. The mindless consumption of natural resources is causing the extinction of several species of flora and fauna. Species like Steller’s sea cow and Passenger pigeons have become extinct due to human exploitation.
- Invasion of Alien Species :
Sometimes, either accidentally or on purpose, alien species which are introduced into certain habitats turn invasive. They end up attacking the indegenous species leading to extinction. The introduction of the Nile Perch into Lake Victoria, in east Africa led to the extinction of 200 species of cichlid fish. Weeds like carrot grass, lantana and water hyacinth are invasive species that cause major environmental damage.
- Climate Change :
Another factor that causes extinction of terrestrial species is climate change. As global temperatures rise, not all species are able to adapt to it. At the end of the last ice-age, most megafauna were unable to survive in the increasing temperatures. They were wiped out by lack of food and were hunted by early humans.
- Illegal Trafficking of Animals :
Animal trafficking, both legal and illegal, has driven countless species to the verge of extinction. Several subspecies of tigers and rhinos are already extinct. The Pangolin is a mammal that is one of the most trafficked in the world. It is estimated that, every year there are around 300,000 species that are being trafficked.
- Pollution :
The pollution being emitted from industries, vehicles and human consumption is severely affecting the planet. Increasing levels of pollution have degraded not only the atmosphere, but also the planet’s water bodies and the ground as well. Use of pesticides and contamination of water bodies have led to the loss of several insect species and marine life.
- Disease :
Epidemics have impacted populations constantly. Over the years, various epidemics have wiped out several human populations, plant and animal species from the planet. Even today, the Covid-19 pandemic has already caused around 3 million deaths around the world. The Black Death decimated over 1/3rd of the European population in the 14th Century.
- Nature of Species :
Some species have a naturally slow birth rate and long gestational periods. This causes a lack of genetic diversity over time leading to extinction. Species like elephants, pandas, and African cheetahs are affected by it.
- Asteroid Impact :
The extinction of dinosaurs was caused by an asteroid strike on the Yucatan peninsula in Mexico around 65 million years ago. An extremely rare event, asteroid or meteor strikes lead to mass extinction of species.
Read more: Ecology
List of Extinct Animals
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There are several species which have become extinct. Some of them are:
- Dodo
- Great Auk
- Steller's Sea Cow
- Tasmanian Tiger
- Passenger Pigeon
- Pyrenean Ibex
- Baiji White Dolphin
- West African Black Rhinoceros.
- Wooly Mammoth
- Saber-toothed Tiger
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| Chapter Related Topics | ||
|---|---|---|
| Mutualism | Predation | Commensalism |
| Homeostasis | Thermoregulation | epiphytes |
Previous Years Questions
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Sample Questions
Ques. Define Extinction. (1 mark)
Ans. Extinction refers to the elimination of a species from the planet. It is a process of evolution that ends the genetic continuity of any given population. Extinction can be caused due to natural calamities, evolutionary changes, and more often, nowadays, due to human interference.
Ques. Name any five causes leading to extinction of species? (2 marks)
Ans. Five major reasons which lead to extinction are:
- Fragmentation of Habitat
- Over-Exploitation of Species
- Climate Change
- Illegal Trafficking of animals
- Asteroid strike
Ques. How can humans prevent extinction of species ? (2 marks)
Ans. There are several steps that can be undertaken to protect threatened species:
- Live a more sustainable life.
- Reduce pollution and release of pollutants in nature.
- Protect wildlife habitats.
- Spread awareness
Ques. What are the types of Extinction ? (2 marks)
Ans. There are two main types of extinction:
- Mass Extinction
- Pseudo Extinction
Ques. When did Dinosaurs become extinct? (1 mark)
Ans. The dinosaurs became extinct during the Cretaceous-tertiary Extinction which took place around 65 Million Years Ago.
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