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Biodiversity, a term popularised by entomologist E.O. Wilson in 1986, denotes the variability among living organisms across three nested levels. Genetic diversity is the variation of genes within a species — the basis of breeds of cattle, the 50,000-plus rice landraces once grown in India, and the resilience that lets populations adapt. Species diversity is the variety of species in a region, measured through richness (count) and evenness (relative abundance). Ecosystem diversity captures the variety of habitats, biotic communities and ecological processes — from the Sundarbans mangroves to the cold desert of Ladakh.
Ecologists distinguish alpha diversity (within a single community), beta diversity (turnover of species between communities along a gradient), and gamma diversity (total diversity across a landscape). The Shannon and Simpson indices quantify alpha diversity.
India holds about 2.4% of the world's land area but roughly 7-8% of recorded species, making it one of 17 megadiverse countries identified by Conservation International (1998). The Wildlife Institute of India recognises 10 biogeographic zones (Trans-Himalaya, Himalaya, Desert, Semi-Arid, Western Ghats, Deccan Peninsula, Gangetic Plain, North-East, Islands, Coasts).
India contains parts of four of the world's 36 biodiversity hotspots defined by Norman Myers (1988, revised 2000): the Himalaya, the Indo-Burma region, the Western Ghats–Sri Lanka, and the Sundaland (Nicobar Islands). A hotspot must have at least 1,500 endemic vascular plant species and have lost 70% or more of its primary vegetation — meaning hotspots are simultaneously the richest and the most threatened areas.
Endemic species occur nowhere else: the lion-tailed macaque and Nilgiri tahr of the Western Ghats, the sangai (brow-antlered deer) of Loktak Lake, Manipur. The IUCN Red List classifies taxa as Extinct, Extinct in the Wild, Critically Endangered, Endangered, Vulnerable, Near Threatened and Least Concern. India's critically endangered species include the Great Indian Bustard, the gharial, the Kashmir stag (hangul) and the pygmy hog.
The principal drivers of biodiversity loss are summarised by the acronym HIPPO (Habitat loss, Invasive species, Pollution, human Population, Overexploitation). Habitat fragmentation is the foremost cause in India; invasive species such as Lantana camara, Prosopis juliflora and the African catfish illustrate the second. The IPBES Global Assessment (2019) warned that around one million species face extinction globally — a high-yield fact for essay and GS-3 answers.
In-situ conservation protects species in their natural habitats and is the preferred strategy because it conserves whole ecosystems and evolutionary processes. Its instruments include Protected Areas under the Wild Life (Protection) Act, 1972 — National Parks, Wildlife Sanctuaries, Conservation Reserves and Community Reserves (the latter two added by the 2002 amendment). India has over 100 national parks and 565-plus sanctuaries. Layered on these are Biosphere Reserves (18, under the UNESCO Man and the Biosphere Programme; Nilgiri was the first in 1986) and Tiger Reserves under Project Tiger (launched 1973) governed by the National Tiger Conservation Authority created by the 2006 amendment.
Ex-situ conservation preserves components outside their habitat: zoological parks and the Central Zoo Authority, botanical gardens, gene banks such as the National Bureau of Plant Genetic Resources (New Delhi), seed banks, cryopreservation and captive breeding (the gharial breeding programme, the pygmy hog project at Basistha, Assam).
The Wild Life (Protection) Act, 1972 is the bedrock statute; its six Schedules grade protection, Schedule I species receiving the highest. The Biological Diversity Act, 2002 implements the Convention on Biological Diversity through a three-tier structure: the National Biodiversity Authority (Chennai), State Biodiversity Boards, and Biodiversity Management Committees at the local level, which maintain People's Biodiversity Registers. The Act regulates access and fair and equitable benefit sharing — the principle vindicated in the Divya Pharmacy v. Union of India (Uttarakhand HC, 2018) ruling upholding benefit-sharing demands on domestic firms.
Internationally, India is party to the CBD (1992), its Cartagena (2000) and Nagoya (2010) Protocols, CITES (1973) regulating wildlife trade, the Ramsar Convention (1971) on wetlands (India had 80-plus Ramsar sites by 2024), CMS (Bonn Convention) on migratory species, and the World Heritage Convention. The Kunming-Montreal Global Biodiversity Framework (December 2022) set the headline '30x30' target — conserving 30% of land and seas by 2030.
Biodiversity is among the highest-yielding areas in Prelims: UPSC repeatedly tests Protected Area locations, species-to-habitat matching, IUCN status, and convention membership (e.g., 2019 on Ramsar wetlands, 2021 on biodiversity-finance). Mains GS-3 frames it under conservation and the environment-development trade-off; questions demand that you connect statutes (WLPA 1972, BDA 2002) to outcomes and to current schemes. Retain three things cold: the four Indian hotspots, the WLPA Protected Area categories, and the three-tier BDA structure. Use the Niyamgiri (Vedanta) Gram Sabha case (Supreme Court, 2013) as a ready example linking biodiversity, tribal rights and the precautionary principle in answer-writing.