MP Board · Class 12 · Biology · Biodiversity and ConservationDiscuss the major causes of biodiversity loss, commonly known as the 'Evil Quartet'. Explain how human activities are accelerating these extinction rates.

Introduction to Biodiversity Loss\nBiodiversity is currently facing accelerated rates of species extinctions, largely driven by human activities. Ecologists have categorized these primary drivers of biodiversity loss into four major causes, aptly termed the 'Evil Quartet'.

1. Habitat Loss and Fragmentation

• Description: This is the most important cause driving animals and plants to extinction. The destruction of natural habitats due to urbanisation, deforestation, agricultural expansion, and mining leaves organisms homeless.
• Impact: When large habitats are broken or fragmented into smaller pieces due to human activities like building highways or constructing buildings, mammals and birds requiring large territories and migratory animals are badly affected, leading to population declines.
• Example: The tropical rain forests, which once covered 14 percent of the earth's land surface, now cover only 6 percent.

2. Over-exploitation

• Description: When human need turns into human greed, it leads to the over-exploitation of natural resources.
• Impact: Many species extinctions in the last 500 years were due to over-exploitation by humans, including stellar's sea cow and passenger pigeon.
• Example: Currently, many marine fish populations are being over-harvested, endangering the continued existence of commercially important species.

3. Alien Species Invasions

• Description: When alien or exotic species are introduced intentionally or unintentionally into a new geographic area, some of them turn invasive and start driving native species to extinction due to the absence of natural predators.
• Example: The introduction of the Nile perch into Lake Victoria in East Africa led to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake. Water hyacinth (Eichhornia crassipes) clogged water bodies and threatened native aquatic life in India.

4. Co-extinctions

• Description: When a species goes extinct, the plant and animal species associated with it in an obligatory relationship also become extinct.
• Example: When a host fish species goes extinct, its unique assemblage of parasites also meets the same fate. In the case of a plant-pollinator mutualism, the extinction of one invariably leads to the extinction of the other.