Complete study notes for BEVAE-181 Block 3 Unit 8. Covers the sixth mass extinction, causes of biodiversity loss (habitat loss, human-wildlife conflict, selective destruction, invasive species, pesticides, climate change), fragile habitats (coral reefs, oceanic islands), the Passenger Pigeon case study, poaching and wildlife trade, invasive alien species in India (water hyacinth, Congress weed, golden apple snail, mesquite), the need for conservation, in-situ vs ex-situ conservation methods, Project Tiger (1973 — 9 to 27 reserves, 268 to 2967 tigers), crocodile conservation, ex-situ methods (botanical gardens, zoos, captive breeding, seed banks, tissue culture), biosphere reserves (UNESCO MAB 1971, 18 in India), and Ramsar wetlands. Includes seven SVG diagrams and model answers. Free PDF download.
Unit 8 · Index
Since 3.5 billion years ago when life began, ~500 million kinds of organisms have lived on Earth. Scientists have documented five mass extinction episodes. Today, growing human population and habitat destruction are driving a sixth extinction. This unit covers causes of biodiversity loss, the urgent need for conservation, and the two main strategies — in-situ and ex-situ conservation — including Project Tiger, biosphere reserves, wetlands, seed banks, and captive breeding.
UN Convention on Biological Diversity estimates ~13 million species still living on Earth, of which only 1.7 million have been identified. Many tropical rainforest species remain undiscovered.
⚠️ The Sixth Extinction: Scientists have documented five mass extinctions in geological history, each caused by catastrophic natural events. Today's extinction rates — driven by human population growth, habitat destruction, and overexploitation — are so high that scientists regard this as the sixth mass extinction episode.
Main causes: land-use changes, changing CO₂ levels, changing climate, biological invasion, and nitrogen deposition (air pollution). Often interrelated.
If an animal's habitat is destroyed, it must adapt, move, or die. When forced out, it competes with existing local populations or migrates into marginal habitat → succumbs to predation, starvation, or disease.
In 1992: ~10% of coral reefs irreparably damaged. 30% expected to suffer damage in 20 years, further 30% loss in next 20–40 years. Tsunami 2004 caused considerable damage to coral reefs of India, Sri Lanka and Thailand. Vulnerable to temperature rise, pollution, and sedimentation.
75% of recorded animal extinctions since 1600 have been on islands. Terrestrial species on isolated oceanic islands more vulnerable due to: restricted ranges, threat from alien species, and island species characteristics (often tame, flightless).
Areas of habitat separated by inhospitable barriers. Freshwater lakes suffer high extinction rates. Among continental extinctions, at least 66% of species loss has been in aquatic habitats.
🌳 Key Fact: More than 3/4 of species endangered today are due to destruction of forest habitats. Tropical rainforests = only 7% of Earth's land but house about 3/4 of total species. Shifting cultivation alone is responsible for 70% of deforestation in Africa, 50% in Asia, 35% in Americas.
Nine of the world's major ocean fisheries are declining (southern bluefin tuna, Atlantic halibut, Pacific salmon). The $10 billion/year global market in wildlife — pets, folk medicines, gourmet foods — threatens elephants, rhinos, sea horses, corals, tropical birds, pandas, and tigers.
The Passenger pigeon (Ectopistes migratorius) was probably the most abundant bird on Earth in the mid-19th century. Flocks darkened the sky during migration — one flock alone was 400 km long with no less than 2 billion birds! There were up to 90 nests per tree across a 5 km × 67 km stretch. In 1871, an estimated 136 million nested in a 2,200 sq.km area in Wisconsin, USA. Their droppings fertilised forests enormously. Today: NOT A SINGLE PASSENGER PIGEON EXISTS. Millions were killed for food every year until the last one died in captivity in 1914.
Burning fossil fuels has dramatically increased CO₂ in the atmosphere → higher global temperatures → rising sea levels → changed climate patterns. The expected speed of climate change + direct habitat loss may prevent species from adapting quickly enough → extinction. Their roles in natural systems will be lost forever.
i) Domesticated animals lose natural survival traits and can spread disease to wild animals (e.g., rinderpest from domestic cattle to Great Indian Rhinoceros). Overgrazing by domesticated herds converts fertile areas into deserts, eliminating wild animals. ii) c) Passenger pigeon iii) a) + c) Habitat destruction and over-harvesting iv) d) All of the above
Jaguar, Tiger, Snow Leopard, Cheetah — hunted for skins. Tiger bones used in traditional medicine.
~90,000 elephants slaughtered per year for ivory tusks. Global market banned by CITES but illegal trafficking continues.
Single rhino horn worth up to $24,000 in black market. Made of keratin (same as fingernails). Used as dagger handles (North Yemen) and powder for fever/aphrodisiac (Asia). 60 countries agreed not to trade — yet illegal trafficking continues!
Hunted for blubber (high-grade oil for lamps) and baleen (for corsets, combs). Blue whale: was 2,00,000 → reduced to 10,000 by mid-1950s. Now protected but may not recover. History = over-exploitation → collapse.
🇮🇳 India's Dubious Record: Among all countries, India has the greatest number of mammalian species on the threatened (endangered, rare etc.) list and in the Red Data Book, India ranks first in the world for threatened mammals.
Invasive/alien/exotic/introduced species = species brought (purposely or accidentally) into new areas where they have few or no natural predators. They cause biological invasions — considered the most important cause of native biodiversity loss after habitat destruction.
Invasive species alter fire cycles, nutrient cycling, hydrology, and energy budgets in native ecosystems. Problem will worsen severely with climate change.
i) b) Congress weed (Parthenium hysterophorus) — its pollen causes skin allergies. ii) Commercial hunting for profit is responsible. Example: Rhinoceros — single horn worth $24,000 in black market. Used for dagger handles (North Yemen) and medicinal powder (Asia) despite being made of keratin. 60 countries banned import/export but illegal trafficking continues. Similarly, 90,000 elephants slaughtered annually for ivory. iii) Water hyacinth introduced in Bengal (1886) as ornamental plant — now covers large water bodies, damages fish and rice crops worth millions of rupees. Parthenium hysterophorus arrived with US food grain imports — reproduces freely from seeds, spread throughout India; pollen causes skin allergies. Invasive species outcompete natives (no natural predators), alter nutrient cycling, hydrology, and are more aggressive under climate change.
"The more biodiversity we destroy and the more irrevocably we change the biosphere, the more we limit our choices for the future."
We cannot know or predict which species will become useful in the future. Every species is a potential resource for medicine, food, and industry.
Biodiversity maintains Earth's life support systems — enabling the biosphere to support human life through nutrient cycling, pollination, water purification, and climate regulation.
It is ethically important to maintain all of Earth's biological diversity, including all extant (currently existing) life forms. Every species has an intrinsic right to exist.
Biodiversity must be conserved at all three levels — genes, species, and ecosystems. Maintaining high genetic diversity ensures species are better adapted and less vulnerable to extinction. Wide ecosystem diversity ensures species have suitable living conditions.
Wildlife conservation is mostly based on in-situ conservation. Protected areas characteristics: Size (bigger = more species), Shape (rounder = less edge effects), Connectivity (corridors allow interbreeding). Buffer zones allow moderate activities (forestry, farming, recreation) — giving local communities economic benefit without harming core.
🇮🇳 India's Protected Areas (as of 2018): 103 National Parks + 536 Wildlife Sanctuaries + 18 Biosphere Reserves. First wildlife sanctuary: Vedanthangal Bird Sanctuary, near Madras, set up in 1878.
The selection of reserves was guided by ecotypical wilderness areas across the biogeographic range of tiger distribution. Project Tiger is custodian of India's major gene pools and repository of valuable ecosystems. The project also saved the Crocodile — Government started Crocodile Breeding and Management Project in 1976 to save all three crocodile species.
🦅 Success Story — Reintroduction: In at least 7 cases, species that were extinct in the wild at time of reintroduction were later successfully re-established: Pere David's deer, Arabian Oryx, American bison, Red wolf, Guam kingfisher, Guam rail, and the California condor. Whooping crane population recovered from 21 birds in 1941 to over 300 in 1996!
i) d) 18 ii) A buffer zone is moderately utilised land that provides a transition into the unmodified natural habitat in the core preserve where no human disturbance is allowed. Buffer zones allow moderate recreational activities, forestry, farming — providing jobs and income to local inhabitants without harming species in the core preserve. They are vital for psychological and practical reasons: local people support conservation only when they derive some economic benefit. By permitting moderate activities, buffer zones reduce pressure on the core area.
Biosphere Reserves are internationally recognised areas to promote and demonstrate a balanced relationship between humans and the biosphere. Initiated under Man and Biosphere (MAB) programme by UNESCO in 1971. Intended to conserve representative ecosystems (not just species or habitats). Provide in-situ conservation of all life forms in totality.
India: 18 Biosphere Reserves. India's first = Nilgiri Biosphere Reserve. World's first biosphere reserve established in 1979. By MAB 2003: 425 reserves in 95 countries. 2 Indian wetlands in first Ramsar Convention (Iran, 1971): Chilka and Bharatpur. Currently 26 Ramsar sites in India.
India's wetlands range from cold arid Ladakh to wet humid Imphal; warm arid Rajasthan to tropical monsoonal Central India. Wetlands perform vital ecological functions:
🌿 Important Indian Wetlands: Kolleru (AP), Wullar (J&K), Chilka (Odisha), Loktak (Manipur), Bhoj (MP), Sambar (Rajasthan), Ashtamudi (Kerala), Harike (Punjab), Dal (J&K). Mangroves: Sunderbans and Andaman & Nicobar Islands hold 80% of India's mangroves (total 6,740 sq.km).
i) d) Seed bank — Seeds have natural dormancy allowing suspended preservation for long periods. Banking dormant seeds of rare/endangered plants keeps genetically representative samples as "genetic insurance." ii) c) Elephants — Elephants do not breed naturally in captivity. A few years ago, the black-footed ferret was down to six individuals but artificial insemination produced 16 kittens. Cheetahs have also conceived. Sperm can be frozen and used later, or transferred to increase genetic diversity.
Exam-style questions from the IGNOU textbook.
Biodiversity is important because:
Global climate change harms biodiversity through multiple pathways: (1) Temperature rise — many species have narrow thermal tolerance windows; rising temperatures force species to migrate poleward or to higher elevations, but species unable to adapt fast enough go extinct. Coral reefs die when ocean temperatures rise even slightly. (2) Rising sea levels — flood coastal and island habitats. 75% of animal extinctions since 1600 have been on islands; rising seas could wipe out remaining island endemics. (3) Altered rainfall patterns — creates more frequent floods and droughts, destroying species habitats. (4) Ocean acidification — CO₂ absorbed by oceans forms carbonic acid, damaging coral reefs and shell-forming marine organisms. (5) Faster than adaptation rate — the expected speed of climate changes, coupled with direct habitat loss, prevents species from adapting quickly enough → extinction and permanent loss of their ecological roles.
In-situ conservation ("on-site"): Protecting endangered species in their natural habitat, either by protecting/cleaning up the habitat or defending species from predators. Benefits: maintains evolutionary processes, allows continued adaptation to surroundings, maintains genetic diversity within natural systems. Examples: National Parks, Wildlife Sanctuaries, Biosphere Reserves, Tiger Reserves.
Ex-situ conservation ("off-site"): Removing species from unsafe habitat and protecting under human care. Limitations: cannot recreate full habitat; costly; inbreeding risk; adaptation problems. Used as last resort or supplement to in-situ. Examples: Botanical gardens, zoos, captive breeding, seed banks, tissue culture.
Ultimate goal of captive breeding: To maintain a viable captive population and eventually reintroduce species back into the wild to bolster or re-establish wild populations. Arabian Oryx, American bison, California condor, and Whooping crane (21 birds in 1941 → 300+ in 1996) are success stories.
Biosphere Reserves are internationally recognised areas to promote and demonstrate a balanced relationship between humans and the biosphere, reconciling conservation with sustainable use. Programme initiated under Man and Biosphere (MAB) programme by UNESCO in 1971.
Structure: Three concentric zones: (1) Core Zone — strictly protected; no human activity; acts as reference for monitoring ecosystem changes. (2) Buffer Zone — moderate activities (research, education, limited tourism) allowed. (3) Transition/Cooperation Zone — human settlements, agriculture, sustainable resource use.
Purpose: Conserve all forms of life in totality (in-situ conservation); serve as referral system for monitoring natural ecosystem changes; provide long-term conservation of plants, animals, and micro-organisms.
India: 18 Biosphere Reserves. India's first = Nilgiri Biosphere Reserve. World total: 425 reserves in 95 countries (MAB 2003). Two Indian wetlands at first Ramsar Convention (Iran 1971): Chilka and Bharatpur. India now has 26 Ramsar sites.
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