Causes of Biodiversity Loss
Environment & Ecology › Threats to Biodiversity and Conservation Strategies · Topic 7.1
Biodiversity is being lost at a rate far above the natural background rate because of human activity. The best-known summary is the evil quartet proposed by Jared Diamond: habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinctions. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES, 2019) ranked five direct drivers by global impact: changes in land and sea use, direct exploitation of organisms, climate change, pollution and invasive alien species. Behind them lie indirect drivers such as population growth, consumption, trade, technology and weak governance. About one million species are threatened with extinction according to IPBES, and monitored wildlife populations have declined by around 70 percent since 1970 according to the Living Planet Index; check the latest edition.
5 min read · UPSC Prelims · Environment & Ecology · Threats to Biodiversity and Conservation Strategies
At a Glance
- Quartet by Jared Diamond
- IPBES report 2019
- Top driver Land and sea use change
- Threatened species About one million
- Index Living Planet Index
- Exam link UPSC Prelims, Environment & Ecology: Threats to Biodiversity and Conservation Strategies
Where Does It Fit?
This is the first topic of the macro on threats and conservation. It sets out why biodiversity is declining before the topics on effects, extinction, the Red List and conservation methods. Previous topic: Marine Mammals, Egg-Laying Mammals and Marsupials. Next topic: Effects of Loss of Biodiversity.
What Are the Main Causes of Biodiversity Loss?
| Cause | Details and examples |
|---|---|
| Habitat loss and fragmentation | The most important cause. Forests cleared for farms, mining, dams and roads; wetlands drained; coral reefs damaged. Tropical rainforests once covered 14 percent of land and now under 6 percent. Fragmentation isolates populations, as in the Amazon and Western Ghats |
| Over-exploitation | Excessive hunting, fishing and harvesting. Steller’s sea cow, passenger pigeon and many fish stocks collapsed. Poaching of tiger, rhino and pangolin, and wildlife trade |
| Alien (invasive) species | Introduced species outcompete natives. Nile perch in Lake Victoria wiped out over 200 cichlid species; water hyacinth, Lantana, Parthenium and African catfish in India |
| Co-extinctions | When a species goes extinct, its dependent species vanish, as with host-parasite or plant-pollinator pairs |
| Pollution | Pesticides, plastics, oil, nutrients and acid rain; DDT thinned eggshells of raptors |
| Climate change | Warming, ocean acidification, shifting ranges, coral bleaching |
| Population and consumption | Indirect driver; rising demand for food, timber and land |
Which Indian Examples and Rates Should Be Remembered?
- Cheetah: declared extinct in India in 1952 due to hunting and habitat loss; reintroduced from Namibia in 2022 and South Africa in 2023
- Pink-headed duck: a possibly extinct bird of eastern India
- Great Indian bustard: critically endangered, with a small population in Rajasthan and Gujarat, hit by power line collisions
- Vultures: crashed over 95 percent in the 1990s due to diclofenac in cattle carcasses
- Wetland loss: a large share of natural wetlands lost in recent decades; check the latest national figures
- Human-wildlife conflict: crop raiding, livestock loss and deaths leading to retaliation
- Wildlife trade: pangolin, star tortoise, tokay gecko and others
- Mining and infrastructure: linear projects fragment habitats and corridors
What Else Should You Remember?
- Jared Diamond: American scientist who named the evil quartet
- Background extinction: natural rate of about one to five species per year; current rates are estimated at 100 to 1,000 times higher
- Sixth mass extinction: a term for the current wave, driven by humans
- Shifting cultivation: jhum leads to forest loss when cycles shorten
- Deforestation: about 10 million hectares lost globally per year in the 2010s; check the Forest Resources Assessment
- Edge effect: fragmented patches have more edge, favouring generalists
- Corridors: strips linking habitats, reducing isolation
- Island species: the most vulnerable to invasives, as with rats on islands
- Mauritius dodo: extinct by the late 1600s due to hunting and introduced animals
- Passenger pigeon: billions once, extinct in 1914
- Overfishing: about a third of fish stocks are overfished, FAO estimates; check the latest report
- Bycatch: unwanted catch such as turtles and dolphins
- Ghost nets: lost nets that keep trapping animals
- Sand mining: harms gharial and riverbed habitats
- Dams: fragment rivers and block fish migration
- Pesticides: affect pollinators; neonicotinoids and bees
- Light and noise: disturb nocturnal and marine species
- Climate migration: species move poleward or uphill and run out of room
- Coral bleaching: repeated marine heat waves
- Invasive Lantana: has overrun many Indian forests
- Alligator weed and mikania: smother native vegetation
- Invasive alien species list: India has many; the Wildlife Protection Amendment Act 2022 gave powers to regulate invasives
- Link to previous: see Marine Mammals, Egg-Laying Mammals and Marsupials
- Link to next: see Effects of Loss of Biodiversity
- Link to invasives: see Environmental Acts, Policies and EIA macro
- Caution: the evil quartet is a Diamond classification, while IPBES uses five drivers; know both
- Exam hint: habitat loss is the top cause for land species and over-fishing for many marine species
Why Does It Matter for the Exam?
- Quartet: habitat, exploitation, aliens, co-extinction
- IPBES: five drivers
- Cases: Nile perch, vultures
- Current affairs link: cheetah reintroduction and invasive species rules
- Common errors: listing pollution in the quartet or ignoring habitat loss as the top cause
As an analytical point, the drivers act together, as habitat loss, climate change and invasives each weaken populations. The remedy must therefore tackle land use and consumption rather than only protect single species.
Why Is This Topic Important?
- Top cause Habitat loss
- Others Exploitation, aliens
- Link Climate, pollution
What Came Next?
The next topic covers the effects of loss of biodiversity. Next topic: Effects of Loss of Biodiversity.
Key People and Terms
- Evil quartet Diamond’s four causes
- Fragmentation Breaking of habitat
- Alien species Introduced non-native species
- Co-extinction Loss of dependent species
- Background rate Natural extinction rate
- Bycatch Unintended catch
Exam Corner
Points to Remember
- Quartet by Jared Diamond.
- Top cause: habitat loss.
- Nile perch hit Lake Victoria.
- Vultures fell due to diclofenac.
- IPBES lists five drivers.
Do Not Confuse With
- Evil quartet and IPBES drivers Four classic causes versus five modern drivers
- Native and alien species Belonging versus introduced
- Extinction and extirpation Global loss versus local loss
Memory Hook
Home, hunt, hitchhikers and hangers-on: habitat, over-exploitation, aliens, co-extinction.
Mains Angle
Questions ask for causes and examples. These points help.
- Causes Quartet
- Examples India
- Response Conservation
A Question You May Face
An original practice question, not a past paper question.
“Discuss the major causes of biodiversity loss with reference to the evil quartet and give examples from India.”
How to Answer
- Quartet Four.
- IPBES Five.
- India Cases.
- Link Interaction.
GS Relevance
Frequently Asked Questions
What is the evil quartet?
The evil quartet is a set of four main causes of biodiversity loss described by Jared Diamond: habitat loss and fragmentation, over-exploitation of species, introduction of alien species, and co-extinctions, where the loss of one species leads to the loss of others that depend on it.
What is the biggest cause of biodiversity loss?
Habitat loss and fragmentation is the largest cause for land species, as forests, grasslands and wetlands are converted to farms, towns, roads and mines. At sea, overfishing and destructive fishing are the main pressure, along with coastal development, and climate change is a fast-growing driver everywhere.
What are the IPBES five drivers of biodiversity loss?
The IPBES 2019 global assessment named five direct drivers in order of impact: changes in land and sea use, direct exploitation of organisms, climate change, pollution, and invasive alien species. These are in turn driven by indirect factors such as population growth, consumption patterns, trade, technology and governance.
How do invasive alien species harm biodiversity?
Invasive alien species have no natural enemies in new places, so they multiply and outcompete, prey on, or infect native species and change habitats. Examples include Nile perch in Lake Victoria, which drove many cichlid fish extinct, and water hyacinth, Lantana and Parthenium in India.
What caused the decline of vultures in India?
The vulture population in India fell by more than 95 percent in the 1990s because they ate carcasses of cattle treated with the veterinary drug diclofenac, which causes kidney failure in vultures. Banning veterinary diclofenac in 2006 and breeding programmes have helped to stabilise some populations.
PYQ Practice — Statement Analysis
1 Habitat loss and fragmentation is the major cause of biodiversity loss.
For most land species.
2 The evil quartet was proposed by Norman Myers.
By Jared Diamond.
3 Nile perch introduction led to loss of cichlid fishes in Lake Victoria.
An alien species case.
4 Diclofenac harmed the vulture population.
Kidney failure.
Past Mains Questions on This Topic
This topic comes under Threats to Biodiversity and Conservation Strategies. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
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