Describe various causes of biodiversity losses in detail.

(N/A) Human activities have accelerated the rate of species extinction from the Earth. The four main causes,collectively known as the 'Evil Quartet',are responsible for the loss of biodiversity:
$(A)$ Habitat loss and fragmentation: This is the most significant cause driving the extinction of both plant and animal species. For example,due to habitat loss,the Earth's land surface covered by tropical rainforests has shrunk from $14 \%$ to only $6 \%$ in recent years. The Amazon rainforest,often called the 'lungs of the planet',is being cleared for soybean cultivation or converted into grasslands for cattle ranching. Additionally,habitat degradation due to pollution threatens many species. When large habitats are fragmented into smaller pieces by human activities,mammals and birds requiring large territories,as well as migratory animals,are severely affected,leading to population declines.
$(B)$ Over-exploitation: Humans have always depended on nature for food and shelter. However,when human needs turn into greed,it leads to the over-exploitation of natural resources. Many species have become extinct in the last $500$ years due to over-exploitation,such as the Steller's sea cow and the passenger pigeon. Currently,many marine fish populations are being over-harvested,threatening the survival of commercially important species.
$(C)$ Alien species invasions: When alien species are introduced unintentionally or deliberately for whatever purpose,some of them turn invasive and cause the decline or extinction of indigenous species. For example,the Nile perch introduced 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.
$(D)$ Co-extinctions: When a species becomes extinct,the plant and animal species associated with it in an obligatory way also become extinct. For example,when a host fish species becomes extinct,its unique assemblage of parasites also meets the same fate.