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What biodiversity is and where it is found

Biodiversity · Part 1 / 2 · Fact-checked on 8 November 2026 · how we check

Written with AI from the sources listed at the bottom of this page, then fact-checked by a separate AI.

The CBD definition and the three levels of biodiversity; species richness and evenness, alpha, beta and gamma diversity; the latitudinal gradient and the species–area relationship; India as a megadiverse country; biodiversity hotspots and India's four; the ten biogeographic zones; endemic species.

The ecology chapter showed how ecosystems work. This chapter asks how much life they hold, where it is concentrated and why it is in danger. biodiversity is a word the Prelims returns to almost every year, through hotspots, endemic species, the IUCN Red List, protected areas and the treaties that protect nature. This first part builds the base: what biodiversity means and its three levels, how ecologists measure it, why it is spread so unevenly over the globe, why India counts among the richest countries, which parts of India are global hotspots, and how the country is divided into biogeographic zones. Part 2 turns to the value of biodiversity, the threats it faces, the Red List and the ways it is conserved.

Biodiversity is short for biological diversity, the variety of all life on Earth. The Convention on Biological Diversity (1992), in its Article 2, defines it as "the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems." Those last words give the three levels that every textbook and every exam uses. genetic diversity is the variety of genes within one species, which is why one crop can exist in hundreds of local varieties and one animal in many breeds. Species diversity is the variety of different species in an area. Ecosystem diversity is the variety of habitats and communities, such as forests, grasslands, wetlands, deserts, mangroves and coral reefs. The three levels are nested: many ecosystems, each with many species, each species carrying many forms of its genes.

Each level matters for its own reason. Genetic variety is the raw material for adapting to change: a population whose members differ can survive a new disease or a hotter climate because some individuals happen to cope. Its loss can be costly. In Ireland in the 1840s, most of the poor depended on potatoes of very few varieties, and when a blight arrived almost the whole crop failed together, contributing to a famine. For the same reason plant breeders value the wild relatives of crops and old farmers' varieties, which carry genes for resistance and hardiness. India is one of the regions where crops such as rice, many pulses, mango and citrus have long been grown and varied, so its traditional varieties are a genetic treasury. Ecosystem diversity matters because each kind of ecosystem supplies its own services: wetlands store floodwater, mangroves shield coasts, forests protect catchments.

Counting diversity is harder than it sounds. The simplest measure is species richness, the number of species in a place. But two forests with twenty species each are not equally diverse if in one forest a single species makes up almost every tree; so ecologists also look at evenness, how equally individuals are shared among species. The American ecologist Robert Whittaker separated diversity by scale. Alpha diversity is the diversity within one habitat or community, such as one patch of forest. Beta diversity is the change in species from one habitat to another, for example as one climbs a mountain or moves from a dry to a wet slope; high beta diversity means neighbouring communities share few species. Gamma diversity is the total diversity of a whole landscape or region, combining the first two. A region like the Western Ghats scores high on all three: rich individual forests, sharp changes over short distances, and a very large overall total.

Life is not spread evenly over the planet. The clearest pattern is the latitudinal gradient: for most groups of plants and animals, the number of species is highest in the tropics and falls steadily towards the poles. A few hectares of Amazon or South-East Asian rainforest can hold more tree species than the whole of a temperate country. Several reasons are offered. The tropics have had a long and relatively stable history, so species have had more time to evolve; their climate varies less through the year, which favours specialists; and they receive more solar energy, which supports higher productivity and so more life. A second pattern links diversity to area. The naturalist Alexander von Humboldt noticed that larger areas hold more species, but not in proportion: richness rises quickly at first and then more slowly. Plotted on logarithmic scales the relationship becomes a straight line, which is why breaking a habitat into small pieces is expected to lose species.

India is one of the world's 17 megadiverse country group, a list drawn up by Conservation International in 1998 of the countries that together hold most of the planet's species. Measured against its size, India is crowded with life: by the figures of the Ministry of Environment, Forest and Climate Change, its share of the planet's recorded species, some 7 to 8 per cent, is about three times its share of land, roughly 2.4 per cent. The reasons lie in its geography. India stretches from tropical islands to the high Himalaya and from the wet north-east to the Thar desert, so it contains almost every major type of ecosystem. It also sits where three great biological realms meet, the Indo-Malayan, the Palaearctic to the north and the Afro-tropical to the west, so its plants and animals have mixed origins. Long isolation of the Peninsula and of islands such as the Andaman and Nicobar group has added species found nowhere else. India is also a member of the Like-Minded Megadiverse Countries group formed in 2002 to coordinate positions in international talks on biodiversity.

Since money and effort for conservation are limited, scientists have tried to identify the places where protection would save the most species. The British ecologist Norman Myers proposed the idea of biodiversity hotspots in 1988, and Conservation International later adopted it with two fixed tests. A region qualifies only if it holds at least 1,500 species of vascular plants found nowhere else in the world, and only if it has already lost at least 70 per cent of its original natural vegetation. The first test measures how irreplaceable the region is; the second measures how threatened it is. Both must be met, so a region that is very rich but still largely intact, such as much of the Amazon, is not a hotspot. There are now 36 hotspots. Together they cover only about 2.5 per cent of the Earth's land surface, yet more than half of the world's plant species are endemic to them, which is why they are seen as the best value for conservation effort.

Four of the 36 hotspots reach into India, and the exam often asks which. The Himalaya hotspot covers the mountain arc from the north-west to the east, with steep changes in climate over short distances. The Indo-Burma hotspot takes in much of India's north-east and runs through Myanmar and South-East Asia; it is rich in orchids, bamboos, primates and freshwater fish. The Western Ghats and Sri Lanka hotspot is a single unit shared with the island across the Palk Strait; the Ghats run parallel to the west coast and stand out for their many endemic amphibians, reptiles and flowering plants. The Sundaland hotspot centres on Malaysia and western Indonesia, and India's share is the Nicobar Islands. A common error is to name the Eastern Ghats, the Thar or the Sundarbans as hotspots: they are important ecosystems but none of them is on the list.

To plan protected areas sensibly, India also needed a map of its own natural regions. The Wildlife Institute of India, in a classification prepared by W. A. Rodgers and H. S. Panwar, divided the country into ten biogeographic zones, each with a distinct mix of climate, landform, plants and animals, and subdivided them further into provinces. The ten are the Trans-Himalaya, the Himalaya, the Indian Desert, the Semi-Arid zone, the Western Ghats, the Deccan Peninsula, the Gangetic Plain, the North-East, the Coasts and the Islands. The Deccan Peninsula is by far the largest. The point of the scheme is representation: a good network of protected areas should include samples of every zone, not just the scenic mountains or famous tiger forests, so that grasslands, deserts and coasts are protected too. The zones also help explain the hotspots, since the Himalaya, the Western Ghats, the North-East and the Islands are the zones richest in species found only there.

An endemic species is one that occurs naturally in a single area and nowhere else; endemism is the share of a region's species that are endemic. Isolation breeds endemics, which is why islands, isolated mountain ranges and old, stable landscapes have many. India's main centres of endemism are the Western Ghats, the north-east, the Himalaya and the Andaman and Nicobar Islands. Examples that the exam likes include the Nilgiri tahr and the lion-tailed macaque of the Western Ghats, the purple frog that spends most of its life underground in the same hills, the Sangai or brow-antlered deer of Manipur's Keibul Lamjao, and the Narcondam hornbill confined to a single small island in the Andaman Sea. The Asiatic lion now survives in the wild only in the Gir landscape of Gujarat. Endemic species carry a special risk: if their small home is damaged there is no other population to fall back on, so a local loss becomes a global extinction.

The ideas in this part fit together as a chain. Biodiversity exists at three nested levels, genes, species and ecosystems, and each level gives life a different kind of insurance. It is measured by richness and evenness and compared within habitats, between them and across regions. It is concentrated in the tropics and in large, varied, isolated areas, which is why India, with its range of climates and its meeting of biological realms, ranks among the megadiverse countries. Hotspots single out regions that are both irreplaceable and badly damaged, and India shares four of them; the ten biogeographic zones make sure that conservation covers every kind of Indian landscape, and endemic species show why losing a small area can mean losing a species for ever. With this map of where life is, Part 2 asks why it is being lost and what is being done to save it.

Exam traps

• The three levels are GENETIC, SPECIES and ECOSYSTEM diversity; varieties of rice or breeds of cattle are genetic diversity, not species diversity.
• ALPHA is within one habitat, BETA is the change between habitats, GAMMA is the total for a region.
• A hotspot needs BOTH tests: at least 1,500 endemic vascular plants AND at least 70% of original vegetation lost. Richness alone is not enough.
• There are 36 hotspots worldwide; India has parts of FOUR: Himalaya, Indo-Burma, Western Ghats and Sri Lanka, Sundaland (Nicobar Islands).
• The Eastern Ghats, the Thar and the Sundarbans are NOT biodiversity hotspots.
• India has about 2.4% of the world's land but about 7–8% of recorded species, and is one of the 17 megadiverse countries.
• India has TEN biogeographic zones; the Deccan Peninsula is the largest.
• Species richness rises with area but not in proportion; it is a straight line only on logarithmic scales.

Recap

• CBD (1992), Article 2: diversity within species, between species and of ecosystems.
• Genetic diversity is the raw material for adaptation; the Irish potato famine of the 1840s shows the cost of losing it.
• Species richness and evenness; alpha (within), beta (between), gamma (regional) diversity, after Whittaker.
• Latitudinal gradient: richest in the tropics; species–area relationship (Humboldt).
• India: one of 17 megadiverse countries; about 2.4% of land, about 7–8% of recorded species; member of the Like-Minded Megadiverse Countries (2002).
• Hotspots: Myers (1988); 1,500 endemic plants and 70% habitat lost; 36 worldwide covering about 2.5% of land.
• India's hotspots: Himalaya, Indo-Burma, Western Ghats and Sri Lanka, Sundaland (Nicobar).
• Ten biogeographic zones (Rodgers and Panwar, WII); Deccan Peninsula largest; endemics such as Nilgiri tahr, lion-tailed macaque, Sangai, Narcondam hornbill.

Practice questions

Sources

• Ministry of Environment, Forest and Climate Change: India's national reports to the Convention on Biological Diversity and the National Biodiversity Action Plan; Botanical Survey of India and Zoological Survey of India material on India's flora, fauna and endemism — https://moef.gov.in
• Convention on Biological Diversity, 1992, Article 2 (Use of Terms) — https://www.cbd.int/convention/text
• Critical Ecosystem Partnership Fund and Conservation International: biodiversity hotspots, criteria and profiles of the Himalaya, Indo-Burma, Western Ghats and Sri Lanka, and Sundaland hotspots — https://www.cepf.net/our-work/biodiversity-hotspots
• Wildlife Institute of India: biogeographic classification of India (Rodgers and Panwar) and the protected area network; ENVIS material on India's biogeographic zones — https://wii.gov.in