Biodiversity and Conservation — NEET Notes

What is biodiversity?

The term biodiversity was popularised by the sociobiologist Edward O. Wilson to describe the combined diversity of life at all levels of biological organisation — from macromolecules within a single cell to entire biomes. It is not one number but a layered idea: the genes inside a species, the species inside a community, and the communities inside an ecosystem all contribute their own grain to the planet's living variety. NCERT treats three of these levels as canonical and the entire NEET syllabus is built on that triad.

"Biodiversity is the combined diversity at all the levels of biological organisation."

Edward O. Wilson — sociobiologist, populariser of the term

Three levels of biodiversity

NCERT names three levels — genetic, species, and ecosystem (or ecological) diversity. Memorise the canonical example for each; NEET tests them directly and through statement-correct questions. India is the textbook illustration of all three.

How many species — on Earth and in India?

The IUCN (2004) records slightly more than 1.5 million described plant and animal species, but the true total is vastly higher — and unknown. Estimates range wildly, from 20 to 50 million. The conservative and scientifically sound estimate by Robert May places global species diversity at about 7 million — the figure NEET 2020 tested directly. More than 70% of described species are animals; plants (including algae, fungi, bryophytes, gymnosperms, and angiosperms) make up no more than 22%. Among animals, insects alone account for over 70% — meaning 7 out of every 10 known animals are insects. Fungi alone outnumber all vertebrate species combined. Prokaryotes are not included in these figures because conventional taxonomy cannot identify most microbial "species"; using molecular criteria, their diversity alone could run into millions.

Patterns of biodiversity

Biodiversity is not spread evenly across the globe. Two NCERT patterns dominate the chapter — the latitudinal gradient (north–south) and the species-area relationship (within a region).

Latitudinal gradient — diversity peaks at the equator

Species diversity decreases as we move from the equator towards the poles. Tropics (latitudinal range 23.5° N to 23.5° S) harbour more species than temperate or polar regions, with very few exceptions. Colombia near the equator has nearly 1,400 species of birds; New York at 41° N has 105; Greenland at 71° N has only 56. India, much of which lies in the tropics, has more than 1,200 bird species. The Amazon rain forest — the largest tropical wilderness on Earth — has the greatest biodiversity on the planet, with 40,000+ plant species, 3,000+ fish, 1,300+ birds, 427 mammals, 427 amphibians, 378 reptiles, and an estimated 1,25,000+ invertebrates. NEET 2020 tested this directly: Amazon is the global maximum.

NCERT lists three hypotheses for why the tropics are so rich:

Species-area relationship

During his explorations of South American jungles, the German naturalist and geographer Alexander von Humboldt observed that within a region, species richness rose with the area sampled — but only up to a limit. The curve, plotted for taxa as varied as angiosperms, birds, bats, and freshwater fishes, turns out to be a rectangular hyperbola. On a logarithmic scale, the same relationship becomes a straight line described by:

log S = log C + Z log A  ⇔  S = C · A^Z

Species-area relationship — S = richness, A = area, Z = slope, C = intercept

The slope Z tells you how steeply richness grows with area, and the value depends entirely on the scale at which you sample. NEET 2017 asked who first described this relationship; the answer is Alexander von Humboldt.

Importance of species diversity to the ecosystem

Does the number of species in a community actually matter to how the ecosystem functions? Ecologists have argued about this for decades. The working consensus, built on two famous lines of evidence, is yes — diversity buys stability.

David Tilman's long-term outdoor plot experiments — running for decades on Minnesota grasslands — showed that plots with more species had less year-to-year variation in total biomass, and that increased diversity contributed to higher productivity. The plots were not just steadier; they grew more. A stable community, in Tilman's operational definition, must (i) not show too much year-to-year variation in productivity, (ii) be either resistant or resilient to occasional disturbances, and (iii) be resistant to invasions by alien species.

Paul Ehrlich's "rivet popper hypothesis" makes the case by analogy. Imagine an airplane (the ecosystem) held together by thousands of rivets (species). If every passenger pops a rivet to take home, flight safety is unaffected at first — but as more rivets disappear, the plane becomes dangerously weak. Which rivet is removed also matters: a rivet from a wing (a keystone species driving major ecosystem functions, in the sense Robert Paine introduced when studying intertidal starfish) is far more critical than a rivet from a window. Two ideas, one conclusion: rich biodiversity is essential for ecosystem health and for the survival of the human race on this planet.

Loss of biodiversity — the sixth extinction

The Earth's biological wealth is declining rapidly. The IUCN Red List (2004) documents the extinction of 784 species in the last 500 years — 338 vertebrates, 359 invertebrates, and 87 plants. Recent examples named in NCERT include the dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller's sea cow (Russia), and three subspecies of tiger — Bali, Javan, and Caspian. The last twenty years alone saw the disappearance of 27 species. More than 15,500 species worldwide currently face extinction: 12% of all birds, 23% of mammals, 32% of amphibians, and 31% of gymnosperms.

Mass extinctions are not new — Earth's fossil record shows five previous episodes. The "Sixth Extinction" now in progress differs not in kind but in rate: current species-extinction rates are estimated to be 100 to 1,000 times faster than pre-human background rates, and human activities are unambiguously responsible. If present trends continue, nearly half of all species could be wiped out within the next century. The downstream consequences for a region losing its biodiversity are NCERT-canonical: (a) decline in plant production, (b) lowered resistance to environmental perturbations such as drought, and (c) increased variability in ecosystem processes — productivity, water use, and pest and disease cycles.

The Evil Quartet — four causes of biodiversity loss

NCERT groups the causes of present-day extinction under a sobriquet: "The Evil Quartet". Memorise all four — NEET has tested every one. The order matters too, because the first one is consistently the most important.

Why should we conserve biodiversity?

NCERT lists three categories of reasons — narrowly utilitarian, broadly utilitarian, and ethical. NEET has occasionally tested these distinctions, especially in statement-based questions on bioprospecting and biopiracy.

• Narrowly utilitarian: the direct economic harvest — food, firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes), and medicines. More than 25% of drugs sold worldwide are derived from plants; 25,000 plant species feed traditional medicine globally. Bioprospecting — exploring molecular, genetic, and species-level diversity for products of economic value — promises enormous benefits to biodiversity-rich nations. NEET 2018 tested the related term biopiracy — the unauthorised use of bioresources by foreign companies — using the Basmati rice patent case as the example.
• Broadly utilitarian: the ecosystem services biodiversity provides — the dwindling Amazon alone is estimated to produce 20% of Earth's atmospheric oxygen via photosynthesis; pollination by bees, bumblebees, birds, and bats underwrites the world's fruit and seed supply; less tangible benefits include flood control, climate moderation, soil formation, and aesthetic value.
• Ethical: every species has intrinsic value regardless of its economic worth. We have a moral duty to pass our biological legacy on in good order to future generations.

How do we conserve biodiversity? In-situ approach

NCERT divides conservation into two strategies — in-situ (on site) and ex-situ (off site). When we conserve and protect the whole ecosystem, biodiversity at all levels is protected — "we save the entire forest to save the tiger." This is the in-situ approach, and NEET 2022 tested this exact definition. India operates a layered network of in-situ protected areas:

Biodiversity hotspots

Because conservation resources are always scarcer than the species needing protection, conservationists identify biodiversity hotspots — regions of very high species richness, high endemism (species confined to that region and found nowhere else), and accelerated habitat loss. The list started at 25 hotspots; NCERT notes that nine more were added, taking the total to 34. More recent global classifications now recognise 36 hotspots worldwide (Forests of East Australia was added in 2011). For NEET, hold both figures in mind — NCERT's 34 is the textbook answer, and the modern count is 36.

Although all hotspots together cover less than 2% of Earth's land area, strict protection of them could reduce the ongoing mass extinction by almost 30%. NCERT names three Indian hotspots — Western Ghats and Sri Lanka, Indo-Burma, and the Himalayas. A fourth — Sundaland, which includes India's Nicobar group of islands — is now standardly added in current biodiversity literature, taking India's count to four.

Sacred groves — India's oldest in-situ tradition

India has a long history of religious and cultural traditions that emphasised the protection of nature. In many cultures, tracts of forest were set aside, and all the trees and wildlife within were venerated and given total protection. These sacred groves survive in five regions named explicitly in NCERT: the Khasi and Jaintia Hills in Meghalaya, the Aravalli Hills of Rajasthan, the Western Ghat regions of Karnataka and Maharashtra, and the Sarguja, Chanda, and Bastar areas of Madhya Pradesh. In Meghalaya, sacred groves are the last refuges for a large number of rare and threatened plants. Crucially, sacred groves are in-situ — NEET 2018 set "sacred groves" as a wrong answer when the question asked which is not ex-situ, and NEET 2019 set "Botanical Garden" as the wrong in-situ option.

Ex-situ conservation

When a species is endangered or threatened — facing very high risk of extinction in the wild in the near future — and needs urgent rescue, ex-situ (off-site) conservation is the desirable approach. Threatened animals and plants are removed from their natural habitat and placed in protected facilities with specialised care. NCERT names the modern toolkit, every item of which has appeared in NEET.

Several species that are extinct in the wild — survive only in zoological parks. The modern ex-situ toolkit goes well beyond enclosures: gametes of threatened species can be preserved indefinitely by cryopreservation; eggs can be fertilised in vitro; whole plants can be propagated by tissue culture (micropropagation); and seeds of commercially important plants are stored long-term in seed banks. NEET 2022 tested this list as a "not ex-situ" question — National Parks was the odd one out.

International efforts — Rio, Johannesburg, and the global framework

Biodiversity knows no political boundaries, and its conservation is therefore a collective responsibility of all nations. The single most-tested international event in this chapter is the Convention on Biological Diversity ("The Earth Summit") held in Rio de Janeiro in 1992. It called upon all nations to take appropriate measures for conservation of biodiversity and sustainable utilisation of its benefits. NEET has asked this fact, in different wordings, in 2019 and 2023.

The 1992 Earth Summit was followed in 2002 by the World Summit on Sustainable Development in Johannesburg, South Africa, where 190 countries pledged to achieve, by 2010, a significant reduction in the global rate of biodiversity loss. India is also a signatory to other key instruments that NIOS and NCERT name: the IUCN (International Union for Conservation of Nature), maintainer of the Red List; CITES (Convention on International Trade in Endangered Species), to which India became party in 1976; and the Ramsar Convention on wetlands of international importance. In India, the Joint Forest Management (JFM) concept, introduced in the 1980s (NEET 2016), brings local communities into the formal management of state forests. The Forest (Conservation) Act, 1980 remains the central statute restricting de-reservation and non-forest use of forest land.