Three levels of biodiversity
The word "biodiversity" was made popular by the biologist Edward Wilson.
- Genetic diversity (variety within a species): Rauwolfia vomitoria in the Himalayas makes different amounts of reserpine; India has more than 50,000 rice and 1,000 mango varieties.
- Species diversity (variety of species): the Western Ghats have more amphibian species than the Eastern Ghats.
- Ecological diversity (variety of ecosystems): India has deserts, rainforests, mangroves, coral reefs, wetlands, estuaries and alpine meadows.
How many species are there?
- IUCN (2004): a little more than 1.5 million species have been described so far.
- Robert May's estimate of the total number of species on Earth: about 7 million.
- More than 70% of all recorded species are animals. Plants (including algae, fungi, bryophytes, gymnosperms and angiosperms) make up no more than 22%.
- Among animals, insects are the biggest group, about 70% of all animals. That means 7 out of every 10 animals are insects!
Patterns of biodiversity
1. Latitudinal gradient: more life near the equator
Diversity decreases as we go from the equator towards the poles.
| Place | Bird species |
|---|---|
| Colombia (near the equator) | ~1,400 |
| India (tropics) | more than 1,200 |
| New York (41° N) | 105 |
| Greenland (71° N) | 56 |
Why are the tropics so rich?
- Long, undisturbed history: the tropics were not frozen by ice ages, so species had millions of years to evolve.
- Stable climate: the tropics are less seasonal and more constant and predictable, so species can specialise.
- More solar energy: more sunlight → more productivity → more food for more species.
2. Species–area relationship
Alexander von Humboldt found that as the area increases, the number of species increases, but only up to a limit.
On a log scale the relationship is a straight line: log S = log C + Z log A
- S = species richness, A = area, Z = slope (regression coefficient), C = Y-intercept.
Z is usually 0.1 to 0.2 for small regions, whatever the group or area.
For very large areas (like whole continents), Z is much steeper: 0.6 to 1.2.
Why is biodiversity important?
Stability of ecosystems
- David Tilman's experiments on outdoor plots: plots with more species had less year-to-year change in total biomass, and higher productivity.
The rivet popper hypothesis
Loss of biodiversity
- The IUCN Red List (2004) records 784 extinctions in the last 500 years, including 338 vertebrates, 359 invertebrates and 87 plants.
- Recent extinctions:
- Dodo (Mauritius)
- Quagga (Africa)
- Thylacine (Australia)
- Steller's sea cow (Russia)
- 3 subspecies of tiger (Bali, Javan and Caspian)
- We are now in the sixth mass extinction. It is happening 100 to 1,000 times faster than before humans, and humans are the cause.
What happens when biodiversity is lost?
- Plant production decreases.
- The ecosystem becomes less stable during disturbances like drought.
- Some processes change: water use, pest and disease cycles.
Causes: the "Evil Quartet"
| Cause | Examples |
|---|---|
| 1. Habitat loss and fragmentation | Tropical rainforests once covered 14% of Earth's land but now cover only 6%. The Amazon ("lungs of the planet") is being cleared for soybeans and cattle grazing |
| 2. Over-exploitation (taking too much) | Steller's sea cow and the passenger pigeon were hunted to extinction. Many marine fish are over-harvested |
| 3. Alien species invasions | Nile perch put into Lake Victoria (East Africa) wiped out more than 200 species of cichlid fish. Weeds like Parthenium (carrot grass), Lantana and water hyacinth (Eichhornia). The African catfish (Clarias gariepinus) threatens native catfish in India |
| 4. Co-extinctions | When a species dies out, species that depend on it also die out. When a host fish goes extinct, its unique parasites go too. A plant and its pollinator can also die out together |
Why should we conserve biodiversity?
| Reason | In simple words | Example |
|---|---|---|
| Narrowly utilitarian | Direct benefits we can use or sell | Food, firewood, fibre, medicines (more than 25% of drugs come from plants), industrial products |
| Broadly utilitarian | Free services from nature | The Amazon produces about 20% of Earth's oxygen; pollination by bees, birds and bats; aesthetic pleasure (bird-watching, walking in a forest) |
| Ethical | Every species has a right to live | We share the planet with millions of species |
How do we conserve biodiversity?
- In-situ (protect it in its natural home): biodiversity hotspots; biosphere reserves, national parks and wildlife sanctuaries; sacred groves.
- Ex-situ (protect it outside its natural home): zoos, botanical gardens and wildlife safari parks; cryopreservation of gametes, seed banks and tissue culture.
In-situ conservation
- Biodiversity hotspots are regions with very high species richness and many endemic species (found nowhere else), which are under threat.
- There are 34 hotspots in the world.
- India has 3 hotspots: the Western Ghats and Sri Lanka, Indo-Burma, and the Himalaya.
- Hotspots cover less than 2% of Earth's land, but protecting them could reduce mass extinctions by up to 30%.
- Protected areas in India: 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries (as given in NCERT).
- Sacred groves: forests protected by local people for religious and cultural reasons. Some rare plants survive only here.
| State | Sacred groves in |
|---|---|
| Meghalaya | Khasi and Jaintia Hills |
| Rajasthan | Aravalli Hills |
| Karnataka and Maharashtra | Western Ghats |
| Madhya Pradesh | Sarguja, Chanda and Bastar areas |
Ex-situ conservation
- Zoological parks, botanical gardens and wildlife safari parks.
- Cryopreservation: gametes of threatened species are frozen and kept alive for a long time using liquid nitrogen at −196 °C.
- In vitro fertilisation and tissue culture to grow plants in labs.
- Seed banks store seeds of many plant varieties.
International efforts
| Event | Year | What happened |
|---|---|---|
| Earth Summit, Rio de Janeiro | 1992 | All nations were asked to protect biodiversity and use it sustainably. This gave the Convention on Biological Diversity |
| World Summit on Sustainable Development, Johannesburg | 2002 | 190 countries pledged to significantly reduce the rate of biodiversity loss by 2010 |
30-second revision
- 3 levels: genetic, species, ecological (Edward Wilson).
- ~1.5 million described (IUCN 2004); ~7 million estimated (Robert May). Insects are about 70% of animals.
- India: 2.4% of land, 8.1% of species; one of 12 mega-diversity countries.
- Diversity falls from equator to poles (time, stability, energy).
- log S = log C + Z log A; Z = 0.1–0.2 (small areas), 0.6–1.2 (continents).
- Rivet popper (Ehrlich); stability (Tilman).
- Evil Quartet: habitat loss (biggest), over-exploitation, alien species (Nile perch), co-extinctions.
- India's 3 hotspots: Western Ghats–Sri Lanka, Indo-Burma, Himalaya. Earth Summit 1992; WSSD 2002.