Name the three important components of biodiversity.

(i) Biodiversity refers to the number and variety of ecosystem species and genetic variation contained within a species. It can also be defined as the totality of a region's genes, species, and ecosystems.

(ii) The estimated total plant and animal species reported on the Earth comes out to be $1.7$ million.

(iii) A rough estimate by many scientists may turn out to be $7$ a million or more, as many species are still undiscovered.

2. Species Diversity:

(i) The group fungi have more species than all the vertebrate species combined.

(ii) India, with $45,000$ species of plants and twice as many species of animals is one of the $12$ mega-diversity countries of the world.

(iii)Diversity at the species level. For example, the Western Ghats have greater amphibian species diversity than Eastern Ghats.

3. Genetic diversity:

Diversity showed by a single species at the genetic level (genetic variation in alleles, entire genes, and chromosomal structures). For example, Rauwolfia vomitoria growing in different Himalayan ranges shows genetic variation in potency and concentration of the active chemical, reserpine. India has more than 50000 genetically diverse strains of rice and 1000 varieties of mango.

4: Ecological diversity:

Diversity at ecosystem (niches, trophic levels, food webs, nutrient cycles, and ecological processes sustaining energy flow) level. For example, in India, many ecosystems like deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows are observed. It is quite less in Scandinavian countries like Norway.

5. Patterns of Biodiversity:

(i) There is greater biodiversity in tropical/subtropical regions than in temperate and polar regions.

(ii) Species diversity decreases from the equator towards the poles.

(iii) Greater number of species in tropical regions is due to good warmth, light and water availability throughout the year.

(iv) The favourable conditions in tropics also contribute to greater productivity.

(v) Species richness is increased with the increasing explored area but only up to a limit.

(vi) A hotspot is that geographical area which is the richest and the most threatened reservoir of plant and animal life on Earth.

(vii) Thirty-four hot spots have been recognised in the world.

(viii) Although all the biodiversity hotspots put together cover less than two per cent of Earth’s land area, the number of species they collectively harbour is extremely high.

6. Causes of Biodiversity Losses:

(i) Earth’s fossil history reveals the incidence of mass extinctions in the past, but the present rates of extinction, largely attributed to human activities, are $100$ to $1000$times higher.

(ii) The causes of high extinction rates at present include habitat loss and fragmentation, invasions of non-native species, over-exploitation, pollution, co-extinctions and climate change.

7. Biodiversity Conservation:

(i) Besides many direct benefits of conserving biodiversity, there are many direct benefits through ecosystem services such as pollination, pest control, climate moderation and flood control.

(ii) In India, biodiversity conservation in situ is carried out by protecting $552$ natural habitats ($14$ biosphere reserves, $90$ national parks and $448$ wildlife sanctuaries).

(iii) Ex-situ conservation practices include protective maintenance of threatened species in zoological parks and botanical gardens.

(iv) The strategies of ex-situ conservation also include in vitro fertilization, tissue culture propagation and cryopreservation of gametes.

(v)The in situ strategies emphasize protection of the whole ecosystem. It is the conservation of genetic resources within natural or human-made ecosystems in which they occur.

(vi) Hot spots: The richest and the most threatened reservoirs of plant and animal life on Earth. The key criteria for determining a hot spot are very high levels of species richness with a high degree of endemism.

(vii) The World Conservation Monitoring Centre (WCMC) had recognized $37,000$ protected areas around the world.

(viii) The $552$ protected areas of India cover about $4.7$ per cent of the land surface as against 10 per cent internationally suggested norms.

(ix A list of endangered plant and animal species is maintained by WCU (formerly known as IUCN).

(x) Species and habitats are legally protected by the efforts of international organizations. The efforts of CITES (Convention on International Trade in Endangered species) in collaboration with UNEP (United Nations Environment Programme) deserve special mention.

(xi) The historic convention on Biological Diversity (The Earth Summit) held in Rio de Janeiro (Brazil) in $1992$.

(xii) In a follow-up of ‘The Earth Summit’, another world summit on ‘Sustainable Development’ was held in $2002$ in Johannesburg, South Africa in which $190$ countries pledged their commitment to conserve biodiversity.