Biodiversity and Conservation

Biodiversity (a term popularised by Edward Wilson) is the variety and variability among all living organisms and the ecosystems they form. It is studied at three levels. Genetic diversity is the variation in genes within a single species — for example, India has thousands of genetically different varieties of rice and mango, and the medicinal plant Rauwolfia shows different potencies (reserpine content) in different regions. Species diversity is the variety of species in an area. Ecological (ecosystem) diversity is the variety of ecosystems / habitats — India, with its deserts, rainforests, mangroves, coral reefs and wetlands, has great ecological diversity.

How many species exist? About 1.5 million species have been described, but the true number is estimated to be much higher; Robert May's conservative global estimate is about 7 million. Among described species, more than 70% are animals, and among animals insects are the most species-rich group. India has about 45,000 plant and 90,000 animal species — roughly 8.1% of the world's species, though India has only about 2.4% of the world's land area, making it one of the megadiverse countries.

Diversity is not evenly spread, and two patterns are heavily examined. The latitudinal gradient: species diversity decreases from the equator toward the poles, so the tropics are the richest (the Amazon rainforest has the greatest biodiversity on Earth). The tropics are richer because they have had a long, undisturbed, warm and productive environment.

The second pattern is the species–area relationship (first noted by Alexander von Humboldt): within a region, species richness increases with the area explored, up to a limit. The relationship is a rectangular hyperbola, which on a log scale becomes a straight line: log S = log C + Z log A (S = species richness, A = area, C = intercept, Z = slope/regression coefficient). The value of Z is about 0.1–0.2 for small areas and rises to about 0.6–1.2 for very large areas (continents). For NEET, fix the three levels (with examples), India's share, the latitudinal gradient (tropics richest), and the species–area equation with typical Z values.

Why does biodiversity matter? The reasons are grouped as narrowly utilitarian (direct economic benefits — food, medicines, fibre, fuel), broadly utilitarian (the ecosystem services like oxygen, pollination and climate regulation), and ethical (every species has intrinsic value and we have a duty to pass on a rich biological heritage). A famous illustration is the 'rivet popper hypothesis' (Paul Ehrlich): an ecosystem is like an aeroplane held together by rivets (species); losing a few rivets (especially key ones) may be tolerated, but losing too many causes the whole system to collapse. Studies (e.g. by David Tilman) also show that communities richer in species are more stable and productive.

Despite this, biodiversity is being lost rapidly — we are living through the Earth's sixth mass extinction, driven by humans. Past natural extinctions and human-caused ones include the dodo (Mauritius), the passenger pigeon and many others.

The major causes of biodiversity loss are summarised as the 'Evil Quartet' — a guaranteed NEET point. The first and most important is habitat loss and fragmentation: the destruction and breaking up of habitats, especially the tropical rainforests (the Amazon, often called the 'lungs of the planet', is being cleared rapidly). The second is over-exploitation — over-harvesting of species (many marine fish, the Steller's sea cow, passenger pigeon).

The third is alien (invasive) species invasions: introduced species that have no natural enemies and out-compete or prey on natives — for example the Nile perch introduced into Lake Victoria caused the extinction of over 200 native cichlid fish; invasive plants like water hyacinth (Eichhornia), Lantana and Parthenium (carrot grass) have also caused harm. The fourth is co-extinctions: when a species goes extinct, the plant/animal species obligately associated with it (e.g. its specific parasite or pollinator) also become extinct. For NEET, fix the reasons biodiversity matters (rivet-popper hypothesis; Tilman's stability) and the four causes of loss in order (habitat loss [biggest] → over-exploitation → alien species → co-extinction) with their examples.

Conservation strategies are of two broad kinds, defined by where the protection happens. In-situ ('on-site') conservation protects species in their natural habitats, conserving the whole ecosystem so that all its species are protected together — this is the preferred approach for large numbers of species.

A key tool of in-situ conservation is the idea of biodiversity hotspots — regions with a very high level of species richness and a high degree of endemism (species found nowhere else), that are also under serious threat. Although the world's hotspots cover less than 2% of the Earth's land, they hold a huge fraction of its species, so protecting them is highly efficient. Originally 25 hotspots were identified (now 34–36); India has three: the Western Ghats and Sri Lanka, the Himalaya, and Indo-Burma.

India also conserves biodiversity through a network of protected areas: biosphere reserves (large, multi-use protected regions — India has 18), national parks (strictly protected, no human activity — over 100) and wildlife sanctuaries (protected but allowing some regulated activity — over 500). These protect species in place.

A beautiful traditional form of in-situ conservation is the sacred grove — forest patches protected by local communities on religious grounds, where felling is forbidden. Famous examples are in the Khasi and Jaintia Hills of Meghalaya, the Western Ghats of Karnataka and Maharashtra, the Aravalli Hills of Rajasthan, and the Sarguja and Bastar areas. Sacred groves harbour many rare and endemic species. For NEET, fix the meaning of in-situ conservation, biodiversity hotspots (high endemism + threat; <2% land; India's three: Western Ghats & Sri Lanka, Himalaya, Indo-Burma), the protected-area types, and sacred groves (Meghalaya).

Ex-situ ('off-site') conservation protects threatened species outside their natural habitats, in specially managed conditions. It is used especially for species that are critically endangered or whose natural habitat is too degraded to protect them in place; it acts as a backup to in-situ conservation, and individuals can sometimes later be reintroduced into the wild.

The traditional ex-situ facilities are zoological parks (zoos), botanical gardens and wildlife safari parks, which keep and breed animals and plants under human care. Modern techniques have made ex-situ conservation far more powerful. Gametes (eggs and sperm) of threatened species can be preserved for long periods by cryopreservation — storage at very low temperature (in liquid nitrogen at −196 °C). Eggs can be fertilised in vitro, and plants can be propagated using tissue culture.

Importantly, seeds of many plants and viable cells can be kept for years in seed banks and gene banks, conserving genetic diversity in a very small space. These methods let us preserve the genetic material of countless species cheaply and safely.

Finally, biodiversity conservation is a global responsibility, addressed by international agreements. At the Earth Summit held in Rio de Janeiro in 1992, nations signed the Convention on Biological Diversity (CBD), pledging to conserve biodiversity and share its benefits fairly. Ten years later, the World Summit on Sustainable Development in Johannesburg (2002) set further commitments to reduce the rate of biodiversity loss. Conservation thus combines in-situ protection of habitats, ex-situ safeguarding of species, and global cooperation. For NEET, fix the meaning of ex-situ conservation, its methods (zoos/botanical gardens, seed/gene banks, cryopreservation at −196 °C, in-vitro fertilisation, tissue culture) and the two global milestones (Rio 1992 → CBD; Johannesburg 2002).