- IUCN Red List (2004) says that 784 species (338 vertebrates, 359 invertebrates & 87 plants) were extinct in the last 500 years. E.g. Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Stellar’s sea cow (Russia) and 3 subspecies (Bali, Javan, Caspian) of tiger.
- 27 species have been disappeared in the last 20 years.
- More than 15,500 species are facing threat of extinction.
- 12% birds, 23% mammals, 32% amphibians, 31% gymnosperm species face the threat of extinction.
- The current extinction rate is 100 - 1000 times faster than in the pre-human times. If this trend continues, nearly 50% species might be extinct within next 100 years.
Impacts of Loss of biodiversity
o Decline in plant production.
o Environmental perturbations such as drought.
o Increased variability in ecosystem processes such as plant productivity, water use and pest & disease cycles.
Causes of Biodiversity losses (‘The Evil Quartet’)
1. Habitat loss and fragmentation: Most important cause.
- E.g. Tropical rain forests (loss from 14% to 6%).
- Thousands of hectares of rain forests are being lost within hours.
- The Amazon rain forest is being cut for cultivating soya beans or for conversion of grass lands for cattle.
- Fragmentation badly affects animals requiring large territories and migratory animals.
2. Over-exploitation: Stellar’s sea cow, Passenger pigeon etc. extinct due to over exploitation.
3. Alien species invasions: Alien species cause decline or extinction of indigenous species. E.g.
- Nile Perch introduced in Lake Victoria (East Africa) caused extinction of more than 200 species of cichlid fish.
- Invasive weed species like Parthenium (carrot grass), Lantana and Eicchornia (water hyacinth) caused damage to our native species.
- Illegal introduction of the African Catfish (Clarias gariepinus) for aquaculture is a threat to the indigenous catfishes in our rivers.
4. Co-extinction: When a species becomes extinct, the species associated with it also extinct. E.g.
- Extinction of the parasites when the host is extinct.
- In co-evolved plant-pollinator mutualism, extinction of one causes the extinction of the other.