Topic 12: Biodiversity Loss & Threats

The direct drivers destroying the world's biodiversity — E.O. Wilson's HIPPO framework, habitat loss vs fragmentation with edge effects and Minimum Viable Population, over-exploitation, India's key invasive alien species, co-extinction cascades, climate change, pollution, and the ecological, food-security and public-health consequences of biodiversity loss.

GS Paper III — Environment & Ecology UPSC Prelims + Mains Very High Importance Reading time: 14 min Updated: July 2026

1HIPPO Framework — Five Drivers of Biodiversity Loss
2Conceptual Clarity — Habitat Loss vs Habitat Fragmentation
3Habitat Fragmentation — Edge Effects, Corridors & MVP
4Over-Exploitation of Species
5Invasive Alien Species
6Co-Extinction
7Climate Change as a Biodiversity Threat
8Pollution & Biodiversity Loss
9Consequences of Biodiversity Loss
10Current Affairs Link
11Prelims PYQs
12Mains PYQs
1315-Minute Revision Box

Conceptual Clarity — Why this Topic Matters

UPSC tests biodiversity loss & threats in three distinct ways:

Definitional / static: exact expansion of HIPPO, the precise difference between habitat loss vs fragmentation, meaning of edge effect, MVP, co-extinction, and CITES appendices — high-frequency single-fact Prelims MCQs.
Statement-elimination: multi-statement sets on invasive-species native ranges (Lantana, Prosopis, water hyacinth), fragmentation properties, and CITES scope where one clause is deliberately reversed.
Applied / current: latest IUCN Red List numbers, new invasive-species alerts, and India-specific eradication drives — link to Mains GS-III conservation-strategy answers (see Current Affairs section).

Focus especially on the HIPPO ranking (habitat destruction = #1), habitat loss vs fragmentation distinction, and India's 8 key invasive alien species with native ranges — the three highest-frequency themes.

1. HIPPO Framework — Five Drivers of Biodiversity Loss

HIPPO is a mnemonic coined by the eminent biologist E.O. Wilson (father of the term "biodiversity") to rank the major anthropogenic drivers of biodiversity loss in descending order of global impact: Habitat destruction, Invasive species, Pollution, Population growth (human), Over-exploitation. Wilson placed habitat destruction first because it is consistently identified as the single largest cause of species extinction worldwide.

Fig 12.1 — HIPPO Framework: the five major anthropogenic drivers of biodiversity loss (E.O. Wilson)

Each HIPPO Letter Explained Individually

H — Habitat Destruction #1 driver

Outright removal or conversion of natural habitat — deforestation for agriculture/plantations, wetland drainage for construction, mining, and unplanned urban sprawl. Removes the physical living space and resource base a species needs entirely.

Example: Large-scale conversion of Western Ghats evergreen forest to tea, coffee and rubber plantations has shrunk lion-tailed macaque and Nilgiri tahr habitat.

I — Invasive Species

Non-native species introduced deliberately or accidentally that establish, spread aggressively and out-compete, predate upon, hybridise with, or transmit disease to native species that have no evolved defence against them.

Example: Lantana camara has invaded over 40% of India's forested Protected Area network, suppressing native undergrowth regeneration.

P — Pollution

Chemical pesticides/heavy metals, plastic waste and nutrient (fertiliser) runoff degrade habitat quality, poison organisms directly, and trigger eutrophication and bioaccumulation up food chains.

Example: Pesticide runoff and industrial effluent along the Ganga-Yamuna basin have depleted native fish and gharial populations.

P — Population Growth (Human)

Rising human numbers increase aggregate demand for land, food, water, timber and energy — the underlying "root driver" that intensifies every other HIPPO factor, especially in high-density, agrarian, forest-fringe regions.

Example: Expanding agricultural frontiers into central Indian forests fragment tiger corridors as village populations and farmland grow.

O — Over-Exploitation

Harvesting wild species (via hunting, fishing, logging, collection) at a rate faster than natural reproduction can replace them, eventually collapsing the population.

Example: Poaching for scales has made the Indian pangolin the world's most illegally trafficked mammal.

UPSC Trap: HIPPO is often mis-recalled with "Population" dropped or replaced. Remember all five letters distinctly: H-I-P-P-O has two P's (Pollution and Population growth) — prelims statement questions frequently test whether a candidate can correctly expand all five components.

2. Conceptual Clarity — Habitat Loss vs Habitat Fragmentation

These two terms are frequently used interchangeably in casual language but are ecologically distinct — UPSC prelims statement questions exploit exactly this confusion, so the distinction must be crystal clear.

The Core Distinction

Habitat loss is a reduction in the total quantity of available habitat — outright destruction or conversion of natural land to another use. Habitat fragmentation is a change in the spatial arrangement of remaining habitat — breaking one large, continuous patch into several smaller, isolated patches, which can happen even without a large net reduction in total habitat area.

Parameter	Habitat Loss	Habitat Fragmentation
What changes	Total area of habitat available shrinks	Spatial configuration/connectivity of remaining habitat changes
Can occur without the other?	Yes — habitat can be lost uniformly without breaking up what remains	Yes — a road/canal can fragment a forest into pieces without removing much total area
Primary mechanism of harm	Removes resources, food and shelter directly	Isolates populations, increases edge effects, blocks migration/gene flow
Typical cause	Deforestation, wetland drainage, mining, urban expansion	Linear infrastructure (roads, railways, canals, power lines), patchy clearing
India example	Clear-felling of forest for a dam reservoir	A highway bisecting a single large tiger reserve into two disconnected halves

UPSC Trap: A statement claiming "habitat fragmentation always causes a net loss of total habitat area" is FALSE — fragmentation is about connectivity/configuration, not necessarily total area lost. In practice the two usually occur together and compound each other, but they are analytically separate processes.

3. Habitat Fragmentation — Edge Effects, Corridors & Minimum Viable Population

Even when total habitat area loss is modest, fragmentation alone degrades biodiversity through several distinct mechanisms operating on the pieces left behind.

Fig 12.2 — Habitat fragmentation over time: contiguous patch (T0) progressively splits into small, edge-dominated, isolated fragments (T2)

How Fragmentation Harms Biodiversity

Edge effects: Smaller patches have a proportionally larger "edge" (boundary zone with altered light, wind, temperature and humidity) relative to undisturbed "core" habitat. Edge zones favour generalist, invasive and predator/nest-parasite species over interior specialists.
Corridor loss: Fragmentation severs the dispersal/migration routes wide-ranging species (elephants, tigers) need to move between patches for feeding, breeding and seasonal movement — the rationale for maintaining wildlife corridors between reserves.
Reduced gene flow: Isolated sub-populations can no longer interbreed freely, raising inbreeding depression risk and reducing genetic diversity, which lowers a population's adaptive capacity.
Minimum Viable Population (MVP) risk: MVP is the smallest sub-population size estimated to have a reasonable statistical chance of long-term survival despite demographic, environmental, and genetic stochasticity. Fragmentation can push isolated sub-populations below their MVP threshold, making local extinction likely even without further habitat loss.

India Case Study — Western Ghats Forest Fragmentation: Roads, hydroelectric reservoirs, monoculture plantations (tea, coffee, eucalyptus) and linear infrastructure have fragmented the once-contiguous Western Ghats rainforest into isolated forest islands. This has restricted lion-tailed macaque troops and Nilgiri tahr populations to small, disconnected patches, prompting active elephant/wildlife corridor restoration projects to reconnect fragments (e.g., corridors linking Anamalai–Parambikulam–Periyar landscapes).

4. Over-Exploitation of Species

Over-exploitation is the unsustainable harvesting of a wild species — for food, medicine, trophies, ornamentation or trade — at a rate faster than its population can naturally replenish, eventually driving numbers to collapse or extinction.

Overfishing

Removing fish faster than stocks can reproduce, collapsing commercial fisheries. Classic example: the collapse of Atlantic cod stocks off Newfoundland in the early 1990s, which has still not recovered decades later.

Overhunting / Poaching

Illegal or unsustainable killing of wildlife for meat, trophies, or body parts. The Indian pangolin is poached for its keratin scales (used in illegal traditional-medicine trade), making it the world's most trafficked mammal.

Overgrazing

Livestock stocking beyond a grassland's carrying capacity strips vegetation cover, compacts soil and prevents regeneration, degrading grassland ecosystems and the wild herbivores dependent on them.

Unsustainable Logging

Timber extraction that exceeds a forest's natural regeneration capacity, removing canopy cover, old-growth trees and associated habitat faster than the forest can regrow — compounds with habitat fragmentation.

Shark Finning

Sharks are caught, their fins sliced off for the shark-fin trade, and the (often still-living) body discarded at sea — a highly wasteful over-exploitation practice that has driven steep global declines in shark populations, which as apex predators destabilises entire marine food webs.

Historical Recap — Passenger Pigeon

Once numbering in the billions across North America, the passenger pigeon was driven to extinction by 1914 through relentless overhunting combined with habitat loss — see Topic 01 (Extinction of Species) for the full case study; it remains the textbook example of how quickly over-exploitation can eliminate even an extremely abundant species.

CITES (1973): The Convention on International Trade in Endangered Species of Wild Fauna and Flora regulates cross-border wildlife trade through three appendices — Appendix I (trade banned, species threatened with extinction), Appendix II (trade regulated/licensed, not yet threatened but could become so), Appendix III (species protected in at least one member country that has asked others for help controlling trade).

5. Invasive Alien Species

An invasive alien species is a non-native organism, introduced deliberately or accidentally outside its natural range, that establishes, spreads aggressively, and causes ecological or economic harm — usually because it lacks the natural predators, competitors, parasites or diseases that kept it in check in its native range.

Mechanisms of Harm

Competition

Out-competes native species for light, water, nutrients, space or prey, suppressing native population growth.

Predation

Preys directly on native species that have no evolved anti-predator defences against the newcomer.

Disease Transmission

Introduces novel pathogens/parasites to which native species have no evolved immunity.

Hybridization

Interbreeds with closely related native species, diluting/eroding the native species' distinct gene pool.

India's Key Invasive Alien Species — Full List

Species	Native Range	Mechanism & Impact in India
Lantana camara	Central/South America	Competition — aggressive flowering shrub invading forest understoreys across the Western Ghats and central India, suppressing native seedling regeneration; invades over 40% of forested Protected Areas.
Parthenium hysterophorus (Congress grass)	North/South America	Competition + allelopathy — releases chemicals that inhibit growth of neighbouring native plants; also causes dermatitis/respiratory allergies in humans and livestock; invades wastelands, roadsides and croplands.
Prosopis juliflora (Vilayati babul)	Central America	Competition — deliberately introduced for afforestation/fuelwood, now an aggressive invader of native grasslands and wetlands, notably the Banni grasslands of Gujarat, displacing native grass cover.
Eichhornia crassipes (Water hyacinth)	South America (Amazon basin)	Competition — floating mat chokes water surface, blocks sunlight, depletes dissolved oxygen through decomposition, disrupting native aquatic plant and fish communities across Indian lakes and canals.
Mikania micrantha (Mile-a-minute weed)	Central/South America	Competition — an extremely fast-growing climbing vine that smothers native vegetation by forming a dense blanket over shrubs and tree canopies, especially damaging in northeast Indian forests and tea estates.
African catfish (Clarias gariepinus)	Africa	Predation — illegally farmed for aquaculture, an aggressive predator that preys on native fish, amphibians and invertebrates when it escapes into Indian rivers/tanks, disrupting native fish communities.
Apple snail	South America	Competition + crop damage — voracious feeder on aquatic vegetation and rice seedlings, out-competing native snails and damaging paddy fields in parts of India.
Red-eared slider turtle	North America (Mississippi basin)	Competition + predation — popular pet trade species released into Indian urban lakes and wetlands, out-competing native turtle species for basking sites and food, and preying on native aquatic fauna.

Pattern to remember: Most Indian plant invasives (Lantana, Parthenium, Prosopis, Mikania) trace back to the Americas and spread via competition/allelopathy; most animal invasives (African catfish, apple snail, red-eared slider) spread via aquaculture/pet-trade escape and act via predation/competition.

6. Co-Extinction

Co-extinction is the phenomenon where the extinction of one species (a "host" or "partner" species) causes a dependent species to also go extinct, because the dependent species relies exclusively on the host for survival or reproduction. It is most pronounced in tightly coupled, specialist ecological relationships.

Obligate Pollinator-Plant Pairs

Fig trees and their species-specific fig wasps are entirely dependent on one another for reproduction — the extinction of either partner in such an obligate mutualism triggers the extinction of the other.

Host-Specific Parasites

Parasites and pathogens adapted to live only on a single host species cannot survive once that host species disappears — e.g., the passenger pigeon's specialist parasitic louse is believed to have gone extinct alongside its host.

Specialist Predator-Prey Pairs

A predator that depends entirely on one declining prey species for food (a dietary specialist with no alternative prey) can be driven to co-extinction if that prey species disappears.

Why it matters: Co-extinction is a key reason biodiversity loss cascades non-linearly through an ecosystem — losing one keystone or highly interconnected species (see Topic 02, Species Interactions) can trigger a chain of secondary extinctions far beyond the immediate direct loss.

7. Climate Change as a Biodiversity Threat

Range shifts: As temperature and precipitation patterns change, species shift their geographic range poleward or upslope in search of suitable climate conditions; alpine and polar species eventually run out of higher ground/latitude — sometimes called the "escalator to extinction."
Phenological mismatch: Climate change decouples the timing of seasonal biological events (breeding, migration, flowering, hatching) between interacting species — e.g., a pollinator emerging before its plant partner flowers — reducing reproductive success for both.
Coral bleaching link: Rising sea surface temperatures cause corals to expel their symbiotic zooxanthellae algae, leading to coral bleaching and reef collapse — coral reefs support roughly a quarter of all marine species, so reef loss cascades into wider marine biodiversity decline.

8. Pollution & Biodiversity Loss

Chemical pesticides, heavy metals, plastic waste and nutrient (fertiliser) runoff degrade habitat quality and poison organisms directly; toxins can bioaccumulate and biomagnify up the food chain, most severely affecting apex predators. Nutrient pollution triggers eutrophication, depleting dissolved oxygen and collapsing aquatic biodiversity.

Cross-link: The full chemistry, sources and control mechanisms of air, water and soil pollution are covered in depth in the dedicated pollution topic files (Topics 21-23) — this section only summarises pollution's role as one of the five HIPPO drivers of biodiversity loss.

9. Consequences of Biodiversity Loss

Ecosystem service degradation: Loss of species weakens pollination, water purification, soil formation, carbon sequestration and natural pest control — services ecosystems provide for free.
Food security risk: Decline of pollinators, fish stocks and crop wild relatives (genetic diversity reservoirs for future crop breeding) directly threatens long-term global food production.
Disease emergence — zoonotic spillover: Habitat destruction and wildlife trade increase human-wildlife contact, raising the risk of pathogens jumping from animals to humans (zoonotic spillover) — a major driver of emerging infectious disease outbreaks.
Economic cost: Biodiversity underpins fisheries, forestry, agriculture, tourism and pharmaceuticals; its loss imposes large, often underpriced economic costs on national and global economies.

UPSC Mains Angle: Always link biodiversity loss consequences back to ecosystem services and human well-being (provisioning, regulating, supporting, cultural services) — this framing scores well in GS-III answers on environment-development trade-offs.

10. Current Affairs Link (2024–2026)

IUCN Red List — 2024–2025 updates check for latest update or data

The IUCN Red List crossed 169,000+ species assessed, with 47,000+ classified as threatened (2025 update). Habitat destruction and invasive species remain the two most-cited threats across taxa. Amphibians stay the most threatened vertebrate class — driven by habitat loss + the invasive chytrid fungus (a co-extinction-adjacent case of an invasive pathogen driving native decline). Verify the newest tally at IUCN before the exam.

India invasive-species eradication drives — 2024–2026 check for latest update or data

Forest/wildlife authorities continued eradication of Prosopis juliflora in the Banni grasslands (Gujarat) and Lantana camara across central Indian tiger reserves under National Action Plans on invasive alien species. ZSI/BSI and state forest departments flagged the spreading red-eared slider turtle and African catfish in urban lakes/wetlands as an escalating threat, driven by pet-trade releases and aquaculture escapes.

Global Biodiversity Framework linkage — 2024 onward check for latest update or data

The Kunming-Montreal Global Biodiversity Framework (GBF) Target 6 specifically commits countries to identify and manage invasive alien species pathways and reduce establishment rates by 50% by 2030 — directly relevant to India's National Biodiversity Strategy & Action Plan (NBSAP) update. Threat-reduction targets under GBF (habitat, invasives, pollution) map onto the HIPPO drivers.

UPSC Relevance: Newly flagged invasive species, updated IUCN threat statistics, GBF threat-reduction targets and India-specific eradication programmes are recurring Prelims fact questions and feed directly into Mains GS-III answers on biodiversity conservation strategy.

11. Prelims PYQs

UPSC Prelims 2023

Q. Consider the following statements regarding invasive alien species in India:

1. Lantana camara is a plant species native to India.
2. Prosopis juliflora was introduced in India for afforestation purposes.
3. Water hyacinth reduces dissolved oxygen levels in water bodies.

Which of the statements given above is/are correct?

(a)1 only
(b)2 and 3 only
(c)1 and 3 only
(d)1, 2 and 3

Ans: (b). Lantana camara is native to Central/South America (not India), so statement 1 is false; Prosopis was introduced for afforestation and water hyacinth depletes dissolved oxygen — both true.

UPSC Prelims 2022

Q. With reference to the "HIPPO" framework of drivers of biodiversity loss, which one of the following correctly expands the acronym?

(a)Habitat destruction, Introduced species, Pollution, Poaching, Overfishing
(b)Habitat destruction, Invasive species, Pollution, Population growth, Over-exploitation
(c)Hunting, Invasive species, Pesticides, Poverty, Overgrazing
(d)Habitat fragmentation, Introduced species, Pollution, Population decline, Overharvesting

Ans: (b). E.O. Wilson's HIPPO = Habitat destruction, Invasive species, Pollution, Population growth (human), Over-exploitation — note the two distinct P's.

UPSC Prelims 2021

Q. Which of the following is an example of "co-extinction"?

(a)Decline of a predator species due to habitat loss
(b)Extinction of a host-specific parasite following the extinction of its host species
(c)Decline of a species due to overhunting
(d)Extinction of a species due to a natural disaster

Ans: (b). Co-extinction's defining feature is a dependent species being lost because its host/partner species goes extinct — the other options are direct, not dependency-driven, extinctions.

UPSC Prelims 2020

Q. Consider the following statements regarding habitat fragmentation:

1. It increases the ratio of edge to core habitat within remaining patches.
2. It can isolate populations and reduce gene flow.
3. It always results in a net loss of total habitat area.

Which of the statements given above is/are correct?

(a)1 and 2 only
(b)2 and 3 only
(c)1 and 3 only
(d)1, 2 and 3

Ans: (a). Fragmentation is about spatial configuration/connectivity — it raises edge:core and cuts gene flow, but does NOT necessarily reduce total habitat area (statement 3 false).

UPSC Prelims 2018

Q. Which of the following is/are covered under CITES?

1. International trade in endangered species of wild fauna and flora.
2. Domestic hunting regulations within a country.
3. Regulation of trade in specimens through a permit system.

Select the correct answer using the code given below:

(a)1 and 2 only
(b)1 and 3 only
(c)2 and 3 only
(d)1, 2 and 3

Ans: (b). CITES regulates cross-border trade via a permit system across its three appendices; it does NOT govern domestic hunting law (that is national legislation like the Wildlife Protection Act).

UPSC Prelims 2016

Q. The Indian pangolin is most frequently poached and illegally traded for which of the following body parts?

(a)Tusks
(b)Horn
(c)Scales
(d)Musk gland

Ans: (c). Its keratin scales are trafficked for illegal traditional-medicine trade, making the pangolin the world's most trafficked mammal.

UPSC Prelims 2014

Q. The cheetah, once found in India, is now considered extinct in the country though it survives in Africa and Iran. This is best described as an example of:

(a)Global extinction
(b)Extirpation (local extinction)
(c)Co-extinction
(d)Pseudo-extinction

Ans: (b). Extirpation = local/regional extinction where the species disappears from one region but survives elsewhere (global extinction would mean gone everywhere).

12. Mains PYQs

Mains GS-III 2022

Q. Discuss the major direct drivers of biodiversity loss globally. Which of these poses the greatest threat in the Indian context, and why? (250 words)

Model Answer Framework

Introduction: Frame direct drivers using E.O. Wilson's HIPPO and note IPBES identifies the same five as the leading anthropogenic causes of decline.
Body — the drivers:
- Habitat destruction (#1 globally) — deforestation, wetland drainage, mining.
- Invasive species — Lantana, water hyacinth out-competing natives.
- Pollution — pesticides, plastics, nutrient runoff/eutrophication.
- Population growth — root multiplier of resource demand.
- Over-exploitation — poaching, overfishing.
Body — greatest Indian threat: habitat loss + fragmentation from infrastructure (roads, dams, railways) and agricultural expansion — e.g. Western Ghats forest islands, fragmented central Indian tiger corridors — compounded by dense human-forest interface.
Conclusion: Landscape-level connectivity planning, eco-bridges, GBF-aligned habitat protection and NBSAP implementation are the priority response.

250 words · 15 marks

Mains GS-III 2020

Q. What are invasive alien species? Discuss their ecological and economic impacts, with examples from India. (250 words)

Model Answer Framework

Introduction: Define IAS — non-native species that establish, spread and cause ecological/economic harm, freed from native predators/competitors (the "enemy release" advantage).
Body — ecological impacts (with India examples):
- Competition/allelopathy — Lantana camara (>40% of forested PAs), Parthenium, Prosopis juliflora (Banni grasslands).
- Predation — African catfish preying on native fish; hybridization diluting native gene pools.
- Aquatic disruption — water hyacinth choking oxygen; red-eared slider displacing native turtles.
Body — economic impacts: crop losses (apple snail in paddy), fisheries decline, clogged waterways/irrigation, high eradication costs.
Conclusion: Need pathway management (GBF Target 6), early-detection-rapid-response, and stricter pet-trade/aquaculture regulation.

250 words · 15 marks

Mains GS-III 2018

Q. Explain the concept of habitat fragmentation and its consequences for biodiversity conservation. Suggest measures to mitigate its impact. (150 words)

Model Answer Framework

Introduction: Define fragmentation (break-up of contiguous habitat into isolated patches) and distinguish it from habitat loss (total area reduction).
Body — consequences:
- Rising edge:core ratio → edge effects favouring generalists/invasives.
- Corridor severance → blocked migration for wide-ranging species (elephant, tiger).
- Reduced gene flow → inbreeding; sub-populations pushed below MVP.
Body — mitigation: wildlife corridors, eco-bridges/underpasses (NH-44 Pench), landscape-connectivity planning, buffer zones, restoration of Western Ghats corridors.
Conclusion: Connectivity-focused conservation is more effective than isolated protected islands.

150 words · 10 marks

Mains GS-III 2016

Q. What do you understand by "co-extinction"? Discuss its significance for biodiversity conservation strategy. (150 words)

Model Answer Framework

Introduction: Define co-extinction — loss of a dependent species triggered by extinction of its host/partner in a tightly coupled relationship.
Body — forms:
- Obligate mutualisms — fig trees & species-specific fig wasps.
- Host-specific parasites — passenger pigeon louse.
- Specialist predator-prey / pollinator-plant pairs.
Body — significance: biodiversity loss cascades non-linearly; losing one keystone/hub species triggers secondary extinctions — argues for ecosystem- and keystone-focused conservation over single-species approaches.
Conclusion: Protecting interaction networks, not just charismatic species, is essential.

150 words · 10 marks

Mains GS-III 2013

Q. Discuss the significance of the CITES convention in regulating international wildlife trade, and India's role as a signatory. (150 words)

Model Answer Framework

Introduction: CITES (1973, in force 1975) regulates cross-border trade in endangered species; India ratified in 1976.
Body — significance & structure:
- Appendix I — trade banned (species threatened with extinction).
- Appendix II — trade regulated via permits (may become threatened).
- Appendix III — species protected in one country seeking others' cooperation.
Body — India's role: obligations met through Wildlife (Protection) Act 1972 schedules; WCCB & customs enforcement; challenges — pangolin scale, shark-fin, star-tortoise trafficking.
Conclusion: CITES + strong domestic enforcement + demand reduction are jointly needed to curb illegal wildlife trade.

150 words · 10 marks

15-Minute Revision Box

Rapid Revision — Biodiversity Loss & Threats

HIPPO (E.O. Wilson)

Habitat destruction (#1 driver) → Invasive species → Pollution → Population growth (human) → Over-exploitation.

Habitat Loss vs Fragmentation

Loss = total area shrinks. Fragmentation = spatial connectivity breaks; can occur without net area loss.
Fragmentation harms via: edge effect ↑, gene flow ↓, corridor blockage, MVP breach.

Over-Exploitation Types

Overfishing (Atlantic cod), overhunting/poaching (Indian pangolin scales), overgrazing, unsustainable logging, shark finning, passenger pigeon (historical).
CITES (1973) — Appendix I (banned), II (regulated), III (country-specific request).

India's 8 Key Invasive Species

Lantana camara, Parthenium hysterophorus, Prosopis juliflora, water hyacinth (Eichhornia crassipes), Mikania micrantha, African catfish, apple snail, red-eared slider turtle.

Co-Extinction

Dependent species goes extinct when its host/partner species is lost — fig-fig wasp, host-specific parasites, specialist predator-prey pairs.

Climate Change & Consequences

Range shifts, phenological mismatch, coral bleaching (~25% marine species dependent on reefs).
Consequences: ecosystem service loss, food security risk, zoonotic spillover, economic cost.

Quick Facts

2025 IUCN update: 169,000+ species assessed, 47,000+ threatened.
Indian pangolin — world's most trafficked mammal (scale poaching).
Lantana camara invades >40% of India's forested Protected Areas.

Letter	Driver
H	Habitat destruction
I	Invasive species
P	Pollution
P	Population growth (human)
O	Over-exploitation

Topic 12: Biodiversity Loss & Threats

Table of Contents

Conceptual Clarity — Why this Topic Matters

1. HIPPO Framework — Five Drivers of Biodiversity Loss

Each HIPPO Letter Explained Individually

H — Habitat Destruction #1 driver

I — Invasive Species

P — Pollution

P — Population Growth (Human)

O — Over-Exploitation

2. Conceptual Clarity — Habitat Loss vs Habitat Fragmentation

The Core Distinction

3. Habitat Fragmentation — Edge Effects, Corridors & Minimum Viable Population

How Fragmentation Harms Biodiversity

4. Over-Exploitation of Species

Overfishing

Overhunting / Poaching

Overgrazing

Unsustainable Logging

Shark Finning

Historical Recap — Passenger Pigeon

5. Invasive Alien Species

Mechanisms of Harm

Competition

Predation

Disease Transmission

Hybridization

India's Key Invasive Alien Species — Full List

6. Co-Extinction

Obligate Pollinator-Plant Pairs

Host-Specific Parasites

Specialist Predator-Prey Pairs

7. Climate Change as a Biodiversity Threat

8. Pollution & Biodiversity Loss

9. Consequences of Biodiversity Loss

10. Current Affairs Link (2024–2026)

11. Prelims PYQs

12. Mains PYQs

Model Answer Framework

Model Answer Framework

Model Answer Framework

Model Answer Framework

Model Answer Framework

15-Minute Revision Box

Rapid Revision — Biodiversity Loss & Threats

HIPPO (E.O. Wilson)

Habitat Loss vs Fragmentation

Over-Exploitation Types

India's 8 Key Invasive Species

Co-Extinction

Climate Change & Consequences

Quick Facts