Biodiversity: meaning, levels, distribution and value

Detail

1. Meaning of biodiversity

• Biodiversity comes from two words: "bio" means life and "diversity" means variety.
• It is the number and variety of plants, animals and micro-organisms, the genes they carry and the ecosystems they form.

• It covers variety within species, between species and between ecosystems.

• It is the result of 2.5–3.5 billion years of evolution. NCERT calls it our "living wealth".

• Species: a group of similar organisms that can breed with each other and produce fertile young (offspring that can also have young).
• Estimates of the total number of species run from 2 million to 100 million.
• About 10 million is the best estimate (NCERT Class 11). Only about 2 million have been described.
• New species keep being found. About 40% of South America's freshwater fishes are still not classified (NCERT).

2. The three levels of biodiversity

Level	What it means	Example	Why it matters
Genetic diversity	Variation of genes inside one species	Differences in human height and skin colour; the many varieties of rice or wheat	Needed for healthy breeding; lets a species adapt to change (new disease, new climate)
Species diversity	Variety of species in an area	Many tree, bird and insect species in a rainforest	Areas with very many species are called hotspots
Ecosystem diversity	Variety of ecosystem types, habitats and processes	Grasslands and sholas (stunted evergreen forest patches in high valleys) of Anamalai, Western Ghats (NCERT Fig. 14.1)	Each ecosystem gives different services to people

• Species diversity is measured in three ways:
• Richness: how many species there are.
• Abundance: how many individuals of each species there are.

• Types: what kinds of species are present.

• Ecosystem boundaries are not sharp. A forest slowly changes into a grassland. So ecosystems are hard to mark on a map.

3. Distribution: where biodiversity is found

• Biodiversity is uneven across the Earth.
• Latitudinal diversity gradient: the number of species is highest in the tropics (near the equator, about 23.5°N to 23.5°S). It falls steadily towards the poles.
• Near the poles: large populations of only a few species (e.g. huge herds of reindeer, few plant types).

• In the tropics: many species, each with smaller numbers.

• Tropical rainforests cover only a small share of the land, but hold about half of all species.

• Why the tropics are richer:
• More solar energy and more water → more plant growth all year → more food for animals.
• Warm, wet climate also causes deep weathering (rock breaking down into soil). This gives thick soils and supports dense forests.
• Stable climate over long periods. The tropics were not covered by ice in the Ice Ages → species had more time to evolve.
• More niches (a niche is a species' "job" and space in an ecosystem). Many layers in a rainforest → room for more species.

Feature	Tropics	High latitudes (near poles)
Number of species	Very high	Low
Population of each species	Small	Large
Solar energy and rain	High, all year	Low, seasonal
Climate history	Stable for long periods	Disturbed by glaciation

4. Endemic species

• An endemic species is found naturally in one area only, and nowhere else in the wild.
• Madagascar (island in the Indian Ocean, off south-east Africa): about 85% of its plants and animals are endemic.
• Indian examples (southern Western Ghats):
• Nilgiri tahr: a mountain goat of the high grasslands of the Nilgiris and Anamalai hills (Tamil Nadu–Kerala).
• Lion-tailed macaque: a monkey of the rainforests of the Western Ghats.

• Humboldtia decurrens: a rare tree of the southern Western Ghats (NCERT Fig. 14.3).

• India ranks high in endemic animals: 10th in birds (69 endemic species), 5th in reptiles (156) and 7th in amphibians (110) [3].

• Endemism is highest in amphibians (61.2%) and reptiles (47%) [3].

5. India: a megadiverse country

• Megadiverse country: one of a small group of countries that together hold most of the world's species.
• India has only about 2.4% of the world's land area, but 7–8% of all recorded species (PIB, 2025) [2][3].
• Recorded species: over 45,500 plants and over 91,200 animals, found in India's ten biogeographic regions (natural zones with their own typical plants and animals) [3]. PIB (2025) gives rounded figures of 45,000 plants and 91,000 animals [2].
• India has 4 of the 34 global biodiversity hotspots [3]:
• Himalaya
• Indo-Burma (North-east India)
• Western Ghats and Sri Lanka

• Sundaland (Nicobar Islands)

• India is one of the eight Vavilovian centres (centres of origin of crop plants, named after the Russian scientist N.I. Vavilov). It has more than 300 wild ancestors and close relatives of crop plants [3].

6. Value of biodiversity

NCERT gives four kinds of value.

(a) Ecological value

• Species do many jobs in an ecosystem:
• They capture and store energy (plants through photosynthesis).
• They make and break down organic matter (decomposers recycle dead material).
• They cycle water and nutrients.

• They fix gases (e.g. CO₂ into plants, nitrogen into soil) and help control climate.

• More diverse ecosystems are more stable and more productive. If one species is lost, others can take over its job.

• Ecosystem services: the benefits people get from nature. The Millennium Ecosystem Assessment (2005) puts them in four groups [4]:

Group	Meaning	Examples
Provisioning	Products we take from ecosystems	Food, water, timber, fibre, medicines [4]
Regulating	Benefits from nature keeping processes in balance	Climate control, flood control, cleaning water, treating waste, stopping erosion [4]
Cultural	Non-material benefits	Spiritual value, recreation, beauty, learning [4]
Supporting	Needed to produce all other services	Nutrient cycling, soil formation, primary production [4]

• Forests are primary producers (they make food from sunlight). All other life depends on them (NCERT Class 10).

(b) Economic value

• Biodiversity gives us food crops, livestock, timber, fish, medicines and cosmetics.
• Agro-biodiversity: the variety of crops, livestock and their wild relatives.
• It is the store of genes used for breeding new plant and animal varieties.

• It is threatened when farmers grow only a few high-yielding varieties (HYVs) → old local varieties are lost → their genes are lost.

• Seeing biodiversity only as a resource also harms it:

• Over-use → species decline.
• Fights over who owns and profits from genetic resources. The Nagoya Protocol (CBD, 2010) deals with this through access and benefit-sharing.

(c) Scientific value

• Each species gives clues on how life began, evolved and keeps working.

(d) Ethical value

• Every species has an intrinsic right to exist (a right of its own, not just because it is useful to people).
• Conservation keeps genetic diversity for agriculture and fisheries (NCERT Class 10).

Prelims Hooks

• The three levels of biodiversity are genetic, species and ecosystem. Differences in human height are an example of genetic diversity, not species diversity.
• Species diversity is measured by richness, abundance and types.
• Sholas and grasslands of Anamalai (Western Ghats) are NCERT's example of ecosystem diversity.
• About 85% of Madagascar's plants and animals are endemic.
• The Nilgiri tahr, lion-tailed macaque and Humboldtia decurrens are endemic to the Western Ghats.
• India has 2.4% of world land but 7–8% of recorded species [2][3]. It has 4 of the 34 hotspots: Himalaya, Indo-Burma, Western Ghats–Sri Lanka, Sundaland [3].
• India's endemism is highest in amphibians (61.2%), then reptiles (47%) [3].
• The MEA (2005) groups ecosystem services as provisioning, regulating, cultural and supporting. Nutrient cycling and soil formation are supporting services, not regulating ones [4].
• Species richness falls from the equator to the poles (latitudinal diversity gradient). Tropical rainforests hold about half of all species.

Mains Points

• Distribution pattern (GS-I): Life is richest in the tropics because of more solar energy and water, a stable climate over long periods and more niches. So the tropical world, including India's Western Ghats and North-east, matters greatly for global conservation.
• India's responsibility (GS-III): India has 2.4% of world land but 7–8% of species, 4 of the 34 hotspots and high reptile and amphibian endemism [2][3]. Losing habitat here means global extinctions. Endemic species need protection where they live (in-situ).
• Agro-biodiversity and food security (GS-III): The spread of a few HYVs since the Green Revolution has pushed out local varieties. India is a Vavilovian centre with 300+ wild crop relatives [3]. Saving them through gene banks, community seed banks and benefit-sharing under the Nagoya Protocol protects future breeding.
• Valuing ecosystem services (GS-III): The MEA (2005) shows that nature also gives regulating, cultural and supporting services, not just goods [4]. Policy should count these services (e.g. flood control by forests and wetlands), not only timber or crops.