There are four major causes of biodiversity loss. These are also known as ‘The Evil Quartet’.
- Habitat loss and fragmentation Destruction of habitat is the primary cause of extinction of species. 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.
- 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.
- 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.
- 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
