The Evil-Quartet

Causes of Biodiversity Losses

i. Habitat loss and fragmentation

1. Destruction of habitat is the primary cause of extinction of species.

2. The tropical rainforests initially covered 14 per cent of the land surface of earth, but now cover only 6 per cent of land area.

3. The Amazon rainforest (called the "lungs of the planet") is being cut and cleared for cultivation of soya beans and for conversion into grasslands for raising beef cattle.

4. When large-sized habitats are broken or fragmented due to human settlements, building of roads, digging of canals, etc., the population of animals requiring large territories and some animals with migratory habitats declines.

ii. Over-exploitation

1. When biological system is over-exploited by man for the natural resources, it results in degradation and extinction of the resources.

2. For example, Stellar's sea cow, passenger pigeon and many marine fishes.

iii. Alien (exotic) species invasions

1. Some alien (exotic) species when introduced unintentionally or deliberately, become invasive and cause harmful impact, resulting in extinction of the indigenous species.

2. Nile perch, a large predator fish when introduced in Lake Victoria (East Africa) caused the extinction of an ecologically unique species of Cichlid fish in the lake.

3. Invasive weed species like Parthenium (carrot grass), Lantana and Eichhornia (water hyacinth) caused environmental damage and posed threat to our native species.

4. Introduction of African catfish (Clarias gariepinus) for aquaculture purposes is posing a threat to the indigenous cat fishes of Indian rivers.

iv. Co-extinctions

1. When a species becomes extinct, the plant and animal species associated with it in an obligatory manner, also become extinct.

2. For example, if the host fish species becomes extinct, all those parasites exclusively dependent on it, will also become extinct; in plant—pollinator mutualism also, extinction of one result in the extinction of the other.