Loss of biodiversity is of great concern. The causes of species extinction, it includes habitat destruction, over exploitation, invasive species, and co-extinction.
1. Habitat loss and fragmentation: Habitat loss is the destruction of ecosystem by unwanted human activities such as urbanization, intensive forming, deforestation, mining etc. Most important example of habitat loss is the tropical rainforests. These forests once covered more than 14% of earth's land surface. Now, they occupy not more than 6% of land area. Forests are the main source of rainfall. They release large amount of water back to the atmosphere through evaporation and transpiration. They are also a storehouse of unique species of medicinal plants and animals. Amazon rain forests commonly called lungs of the planet is being cut and cleared for soyabeans cultivating and grassland development.
2. Overexploitation: Humans are always dependent on nature for food and shelter, but when need tunes to greed, it leads to overexploitation of natural resources on the name of development. The different types of over exploitation include over grazing, overfishing, over cultivation. For example Stellar's sea cow, passenger pigeon were due to over exploitation by humans.
3. Alien species invasions: When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive, and cause decline or extinction of indigenous species. The Nile perch introduced into Lake Victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake. You must be familiar with the environmental damage caused and threat posed to our native species by invasive weed species like carrot grass, Lantana and water hyacinth. The recent illegal introduction of the African catfish Clarias gariepinus for aquaculture purposes is posing a threat to the indigenous catfishes in ours rivers.
4. Co-extinctions: It is the simultaneous extinction of two or more species when one is dependent on the other' Ex: If humming birds become extinct, the mites would also become extinct. Plants becomes extinct, the animals would also become extinct. Host become extinct, the parasites would also become extinct.