Biodiversity is the variety of living forms present in various ecosystems. It includes life forms from all sources including land, air and water. The three important components of biodiversity are genetic diversity, species diversity and ecosystem diversity. Biodiversity is declining at a very fast rate around the world. The four major causes of loss of biodiversity are:
1) Habitat loss and fragmentation- This is the most important reason causing the extinction of plants and animals. The habitats of various plants and animals are destroyed by uncontrolled human activities such as deforestation, mining, urbanization, etc. Due to these activities, the movement of migratory animals is affected and the genetic exchange between populations decreases leading to a declination of species.
2) Overexploitation- Many species extinctions in the last 500 years were due to the overexploitation and overhunting of various plants and animals by humans. Most industrial fisheries are either fully or overexploited, and the impacts of overharvesting are coupled to destructive fishing techniques that destroy habitat.
3) Alien species invasion- A declination or extinction of indigenous species is caused by the accidental or intentional introduction of non- native species into a habitat. Example: Introduction of Nile perch in Lake Victoria in Kenya led to the extinction of more than two hundred species of native fish in the lake.
4) Co-extinction- In a habitat, on species is connected to the other species in an intricate network. The extinction of one species causes the extinction of the other species. Example: The extinction of the host will cause the extinction of its parasites.
The adverse effects on native species on an invasion of alien species in a habitat-
1) Due to vigorous growth and competition of alien species with the natural species of minerals, water, etc; the less vigorous local species may get eliminated.
2) The introduced alien species may harm the local species by the production of chemicals.
3) The alien species may make conditions unfavourable for the growth of local native species.