Introduction & Levels of Biodiversity
- The term Biodiversity was popularized by Edward Wilson to describe diversity at all levels of biological organisation.
- Genetic Diversity: Variation within a single species at the genetic level.
- Example: Rauwolfia vomitoria in the Himalayas shows genetic variation in the concentration of the active chemical reserpine.
- India has >50,000 different strains of rice and >1,000 varieties of mango NEET 2011.
- Crucial Detail: Maximum genetic diversity in India is shown by Rice AIPMT 2009 NEET 2011.
- Species Diversity: Diversity at the species level (e.g., Western Ghats have greater amphibian species diversity than Eastern Ghats).
- Ecological Diversity: Diversity at the ecosystem level (e.g., India's deserts, rain forests, mangroves, coral reefs, wetlands).
Global Species Diversity (Number of Species)
- IUCN (2004) Data: More than 1.5 million species have been described so far.
- Robert May's Estimate: Global species diversity is estimated at about 7 million NEET 2020 2024. Only 22% of total species have been recorded so far.
- Animal vs. Plant Ratio: Animals constitute >70% of all recorded species, while plants (including Plantae and Fungi) make up only 22%.
- Insects dominance: Insects are the most species-rich taxonomic group, making up 70% of all animals (7 out of every 10 animals are insects) NEET 2011. Arthropoda represents the largest phylum of Animalia NEET 2011.
- Exception/Crucial detail: The number of Fungi species in the world is greater than the combined total species of fishes, amphibians, reptiles, and mammals NEET 2013.
- Biodiversity in India: India possesses 2.4% of the world's land area but harbours 8.1% of global species diversity, making it one of the 12 mega diversity countries.
- Prokaryotic caveat: Biologists cannot accurately estimate prokaryotic diversity because conventional taxonomic methods are unsuitable for microbes, and many cannot be cultured in a laboratory.
Global Biodiversity Proportions (Pie Charts Representation)
NEET 2014
| Taxa Group | Order of Abundance (Highest to Lowest) |
|---|---|
| Invertebrates | Insects > Other animal groups > Molluscs > Crustaceans |
| Vertebrates | Fishes > Birds > Reptiles > Amphibians > Mammals |
| Plants | Fungi > Angiosperms > Algae > Mosses > Ferns & allies > Lichens |
Patterns of Biodiversity
Latitudinal Gradients
- Species diversity generally decreases from the equator towards the poles. Tropical rain forests are richest in species diversity AIPMT 1990.
- Tropical region (Ecuador) has up to 10 times more vascular plant species than temperate regions (Midwest USA).
- Amazonian Rain Forest (South America): Holds the greatest biodiversity on Earth NEET 2020. Abundance order: Plants (>40,000) > Fishes (3,000) > Birds (1,300) > Mammals (427) = Amphibians (427) > Reptiles (378) > Invertebrates (>1,25,000) NEET 2022.
Why Tropics have High Biodiversity?
NEET 2024
- More evolutionary time: Tropics remained undisturbed by glaciations, allowing long time for species diversification.
- Less seasonal/More constant: Stable environments promote niche specialization.
- More solar energy: Leads to higher productivity.
- Crucial Detail: Frugivorous birds are found in large numbers in tropical forests primarily due to the availability of fruits throughout the year in a constant environment NEET 2022.
Species-Area Relationship
- Formulated by German naturalist Alexander von Humboldt based on studies in South American jungles NEET 2017 2020 2024.
- Species richness increases with increasing explored area, but only up to a limit.
- The relationship is a rectangular hyperbola: S = CAz.
- On a logarithmic scale, it is a straight line: Log S = log C + Z log A.
- Z-value (Slope of the line): For small areas, Z = 0.1 to 0.2 (regardless of taxa/region). For large areas like entire continents, the slope is much steeper with Z = 0.6 to 1.2. For frugivorous birds and mammals in tropical forests, Z = 1.15.
Importance & Loss of Biodiversity
- David Tilman's Ecosystem Experiments: Plots with higher species diversity showed less year-to-year variation in total biomass and contributed to higher productivity NEET 2024.
- Rivet Popper Hypothesis: Proposed by Paul Ehrlich to explain the importance of species diversity NEET 2024.
- Airplane = Ecosystem; Rivets = Species NEET 2022.
- Popping rivets on the wings (key species) is far more dangerous to flight safety (ecosystem functioning) than popping rivets on seats.
- IUCN Red List: Publishes data on threatened species AIPMT 1999 AIPMT 2006 NEET 2014.
- Recent extinctions: Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Stellar's sea cow (Russia), and 3 tiger subspecies (Bali, Javan, Caspian). Recently extinct from India is Cheetah (Acinonyx) AIPMT 1998.
- A species facing extremely high risk of extinction in the immediate future is categorized as Critically Endangered NEET 2014.
- Threatened Groups: 12% birds, 23% mammals, 31% gymnosperms, 32% amphibians. Among vertebrates, mammals comprised the highest number of endangered species (based on early PYQ data) AIPMT 2003.
Causes of Biodiversity Loss (The Evil Quartet)
NEET 2019 2022 2023 2024
- Habitat Loss and Fragmentation: The most important cause driving animals and plants to extinction NEET 2016 2023 2024.
- Example: The Amazon rain forest is being cut and cleared for cultivating soya beans or converting to cattle pasture NEET 2022. Fragmentation severely affects migratory animals and those requiring large territories.
- Over-exploitation: Humans driven by greed lead to extinction. Examples: Stellar's sea cow, Passenger pigeon.
- Alien Species Invasions: Causes decline or extinction of indigenous species NEET 2024.
- Nile Perch introduced into Lake Victoria (East Africa) led to the extinction of >200 species of cichlid fish NEET 2022.
- Invasive weeds like Parthenium (carrot grass) NEET 2016 2024, Lantana, and Eichhornia (water hyacinth) damaged native species AIPMT 2007.
- Illegal introduction of African Catfish (Clarias gariepinus) threatens indigenous catfishes.
- Co-extinctions: When a host becomes extinct, its obligate parasites also extinct (e.g., co-evolved plant-pollinator mutualism).
Biodiversity Conservation Concepts
- Endemic Species: Species confined to a particular region and not found anywhere else NEET 2015 2022. Occurrence of endemic species in regions like South America and Australia is largely due to continental separation AIPMT 2001.
- Keystone Species: A species that makes up only a small proportion of total biomass, yet has a huge impact on community organisation and survival AIPMT 2004.
- Chipko Movement: Launched for the protection of forests NEET 2009.
In-Situ vs. Ex-Situ Conservation
| Conservation Strategy | Key Characteristics | Examples (High-Yield NEET Factoids) |
|---|---|---|
| In-Situ Conservation (On-site) NEET 2019 2022 2024 | Protecting the endangered species by conserving the whole ecosystem in its natural habitat. |
National Parks: Strictly reserved for wildlife welfare (no grazing/private ownership). E.g., Jim Corbett (Tiger) AIPMT 1995 AIPMT 2006, Kaziranga (Rhino) AIPMT 2006 NEET 2010. Sanctuaries: E.g., Periyar (Elephant). Biosphere Reserves: Includes a legally protected Core Zone where no human activity is allowed NEET 2017. Sacred Groves: Khasi & Jaintia Hills (Meghalaya) NEET 2022 2024, Aravalli Hills (Rajasthan). |
| Ex-Situ Conservation (Off-site) NEET 2014 2015 2017 2018 2024 | Threatened organisms are taken out of their natural habitat and placed in special settings where they are protected. |
Zoological Parks & Botanical Gardens: Allow ex-situ conservation of germplasm AIPMT 2004 AIPMT 2005. Wildlife Safari Parks. Advanced Methods: Cryopreservation (preserving gametes/viable material in fertile condition for long periods) NEET 2015 2024. Seed banks/Gene banks NEET 2015. Tissue culture/Micropropagation NEET 2013 2015. |
Biodiversity Hotspots
- Regions with very high species richness, high degree of endemism, and accelerated habitat loss NEET 2024.
- 34 hotspots globally identified by Norman Myers NEET 2016. They cover <2% of earth's land area but can reduce ongoing mass extinctions by almost 30%.
- India has 3 hotspots: Western Ghats & Sri Lanka, Indo-Burma, and Himalaya. (Western Ghats is a heavily tested hotspot) AIPMT 2006 NEET 2012.
International Conventions and Acts
- The Earth Summit (1992): The historic Convention on Biological Diversity held in Rio de Janeiro. Its 3 objectives: Conservation of biodiversity, sustainable utilization of its benefits, and sharing benefits arising from genetic resources NEET 2019 2023 2024.
- World Summit on Sustainable Development (2002): Held in Johannesburg, South Africa. 190 countries pledged to achieve a significant reduction in the current rate of biodiversity loss NEET 2022 2024.
- Biodiversity Act of India: Passed by the Parliament in the year 2002 AIPMT 2005.