Biodiversity and Conservation - Notes | Class 12 | Part 2: Loss of Biodiversity



- 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.


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