Causes of Biodiversity Losses

i. Habitat loss and fragmentation 

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

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

ii. Over-exploitation 

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

• For example, Stellar’s sea cow, passenger pigeon and many marine fishes.

iii. Alien (exotic) species invasions 

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

• 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.

iv. Co-extinctions

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

• 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 results in the extinction of the other.