The biological wealth of our planet has been declining rapidly and the accusing finger is clearly pointing to human activities. The colonisation of tropical pacific islands by humans is said to have led to extinction of more than 2000 species of native birds. The IUCN red list documents the extinction of 784 species. Since the origin and diversification of life on earth, there were five episodes of mass extinction of species. Current species extinction rate as estimated to be 100-1000 times faster. There are four major causes called “The Evil quartet” Habitat loss, over exploitation, Alien species invasion and co-extinction. Conservation efforts are necessary to preserve biodiversity and protect endangered species and their habitats.

Mr. X wants to understand the ‘Evil Quartet’ to know the reasons of Biodiversity loss. It is :

Habitat loss, over exploitation, Alien species invasions and co-extinctions

The correct answer is Option (4) -Habitat loss, over exploitation, Alien species invasions and co-extinctions

There are four major causes of biodiversity losses called ‘The Evil Quartet’. These are habitat loss and fragmentation, over exploitation, alien species invasions and co-extinctions.

Habitat loss and fragmentation: This is the most important cause driving animals and plants to extinction. The most dramatic examples of habitat loss come from tropical rain forests. Once covering more than 14 per cent of the earth’s land surface, these rain forests now cover no more than 6 per cent. They are being destroyed fast.

Over-exploitation: Humans have always depended on nature for food and shelter, but when ‘need’ turns to ‘greed’, it leads to over -exploitation of natural resources. Many species extinctions in the last 500 years (Steller’s sea cow, passenger pigeon) were due to over -exploitation by humans.

Alien species invasions: When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive, and cause decline or extinction of indigenous species. The Nile perch introduced into Lake Victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake. Other examples of invasive weed species like carrot grass (Parthenium), Lantana and water hyacinth (Eicchornia). The recent illegal introduction of the African catfish Clarias gariepinus for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.

Co-extinctions: When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct. When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate. Another example is the case of a co-evolved plant-pollinator mutualism where extinction of one invariably leads to the extinction of the other.