Loss of biodiversity: drivers and evidence

Detail

1. Why biodiversity loss is speeding up

• Loss of biodiversity means the fall in the number of genes, species and ecosystems on Earth. Biodiversity has fallen fast since humans appeared.
• People and consumption drive the loss:
• more people → more food, wood, land and minerals needed
• higher consumption → more forest cleared and more animals hunted

• result → species lose their homes and die out faster

• The tropics are where pressure and richness overlap:

• The tropics lie between the Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S).
• They cover about one-quarter of the world's area but hold about three-quarters of its people.
• The same tropics hold about half of all species.
• So over-use of resources and deforestation are worst exactly where most species live.

2. Habitat loss: the biggest driver

• Habitat loss means a plant or animal's natural home is destroyed, reduced or broken into small pieces.
• Habitat fragmentation means a large forest or grassland is cut into small, separate patches by farms, roads or settlements. Animals in small patches cannot find mates, food or space.
• Main causes:
• clearing forests and grasslands for farms
• logging (cutting trees for timber)
• mining

• settlements and roads

• Global scale (IPBES 2019):

• about 75% of the land environment has been "severely altered" by human actions [3]
• about 66% of the marine (sea) environment has been significantly altered [3]
• more than 85% of the wetlands that existed in 1700 had been lost by 2000 [3]

3. Other causes of loss (Class 11)

Cause	What it means	Examples
Natural calamities	Sudden natural events that destroy plants and animals	Earthquakes, floods, volcanic eruptions, forest fires, droughts
Pesticides and pollutants	Poisons that build up in soil, water and living bodies	Pesticides, hydrocarbons (oil, petroleum products), heavy metals (lead, mercury, cadmium)
Local over-use (Natural Vegetation chapter)	Daily human pressure on forests	Lopping trees for fodder and fuel, overgrazing by cattle, forest fires
Sport hunting	Killing animals for fun or status, often by the elite	Historic hunting of tigers, cheetahs and birds
Plastic pollution	Waste that chokes and poisons sea life	Plastic pollution has grown 10 times since 1980 [3]

4. Exotic species and invasive alien species

• Exotic species: a species brought into a habitat where it does not occur naturally. The move may be on purpose (gardens, fish farms) or by accident (in ships, with grain).
• Invasive alien species (IAS): exotic species that spread fast and harm native plants, animals, ecosystems or people's livelihoods.
• How an invasive species takes over:
• it arrives in a new place with no natural enemies (no predators or diseases)
• it grows and breeds faster than native species

• it takes over light, water, food and space → native species decline

• Indian examples:

Species	Type	Where it harms in India
Lantana camara	Shrub	Forests across India, including tiger reserves; blocks grass and tree seedlings
Prosopis juliflora	Thorny tree	Banni grasslands, Kachchh (Gujarat); turns grassland into thicket and reduces fodder
Water hyacinth	Floating water plant	Lakes, ponds and canals; covers the water surface and cuts oxygen for fish
Parthenium (congress grass)	Weed	Farmland and wasteland; harms crops and causes allergies
Mikania	Climbing vine	Forests of the North-East and Western Ghats; smothers trees
African catfish	Fish	Rivers and wetlands; eats native fish

• Island species are most at risk. Class 11 gives the example of Hawaii (Pacific Ocean): native island species there are threatened by introduced species. Island species evolved without many predators, so they have little defence.
• IPBES Invasive Alien Species Assessment (2023):
• invasive species played a part in about 60% of recorded extinctions

• they cost the world over US$423 billion a year

• In the IPBES 2019 ranking, invasive species are the fifth of five direct drivers [3].

5. Poaching

• Poaching means illegal hunting or capturing of wild animals.
• Targets and body parts:

Animal	Part taken
Tiger	Skin, bones
Elephant	Tusks (ivory)
Rhinoceros	Horn
Crocodile	Hide (skin)
Minks and birds	Fur, skins, feathers

• Poaching is a form of direct exploitation, which IPBES ranks as the second biggest driver of loss [3].

6. Overfishing

• Overfishing means catching fish faster than they can breed and replace themselves.
• How overfishing collapses a stock:
• too many fish caught, including young ones
• too few adults are left to lay eggs

• the fish population (the "stock") shrinks and may collapse

• Global evidence:

• IPBES (2019): 33% of marine fish stocks were harvested unsustainably in 2015; 60% were fished at the maximum sustainable level and only 7% were under-fished [3]
• FAO (2025 review, 2,570 stocks assessed): 35.5% of stocks are overfished and 64.5% are sustainable [4]
• By catch volume, 77.2% of landings come from sustainable stocks [4]
• Overfishing has risen by about 1% a year on average in recent years [4]

• Weakest regions: Mediterranean and Black Sea (only 35.1% of stocks sustainable) and South-east Pacific (46%). Best regions: Antarctic (100%) and North-east Pacific (92.7%) [4]

• India's response: the 61-day uniform fishing ban

• It applies in India's EEZ (Exclusive Economic Zone: the sea belt from 12 to 200 nautical miles where India alone may fish and mine), beyond territorial waters [2]
• East coast: 15 April to 14 June [2]
• West coast: 1 June to 31 July, during the south-west monsoon [2]
• It covers the breeding (spawning) season, so fish can lay eggs and the stock can recover
• Traditional non-motorised boats are exempt [2]
• The Department of Fisheries fixes it each year on a Technical Committee's advice, after talking to coastal States and UTs [2]

7. Extinction and its rate

• Extinction: the permanent loss of a species. No member is left alive anywhere.
• Background (natural) extinction:
• about 99% of all species that ever lived are now extinct
• an average species lasts 1–4 million years

• the background rate is the slow, natural rate at which species die out without humans

• Human-driven extinction:

• the current extinction rate is tens to hundreds of times higher than the average over the last 10 million years, and it is still rising [3]

• "Sixth mass extinction" debate:

• A mass extinction is a short period in which a large share of all species dies out.
• Earth has had five. The latest, at the end of the Cretaceous, wiped out the dinosaurs.
• Many scientists argue that human activity is now causing a sixth. Others say the losses so far are not yet big enough to count as one. Both sides agree that extinction rates are far above normal.

8. Evidence: IPBES Global Assessment (2019)

• IPBES (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services): a body of governments set up in 2012. It reviews the science on nature for policy makers. It is often called the "IPCC for biodiversity".
• 2019 Global Assessment: written by 145 expert authors from 50 countries, with 310 contributing authors, drawing on about 15,000 sources [3].
• Headline finding: up to 1 million species face extinction, many within decades [3].
• Threatened shares:

Group	Share threatened
Amphibians	More than 40%
Reef-forming corals	About 33%
Marine mammals	More than 33%
Insects (tentative)	About 10%
Average across groups studied	About 25%
[3]

• The five direct drivers, ranked (highest impact first) [3]: 1. Changes in land and sea use 2. Direct exploitation of organisms (hunting, fishing, logging) 3. Climate change 4. Pollution 5. Invasive alien species

9. Evidence: Living Planet Report (WWF, 2024)

• Living Planet Report: a report published by WWF every two years. It tracks average changes in wild vertebrate populations (mammals, birds, fish, reptiles, amphibians) using the Living Planet Index.
• 2024 findings (period 1970–2020):
• monitored vertebrate populations fell by an average of 73%
• Latin America and the Caribbean: a 95% fall, the steepest of any region

• Freshwater populations: an 85% fall, the steepest of any ecosystem type

• Exam caution: the index measures the average fall in population size. It does not mean that 73% of animals or species have disappeared.

Prelims Hooks

• IPBES (set up 2012) driver ranking, highest to lowest: land and sea use change > direct exploitation > climate change > pollution > invasive alien species. Climate change is third, not first.
• India's 61-day fishing ban: East coast 15 April–14 June; West coast 1 June–31 July. It applies in the EEZ, and traditional non-motorised boats are exempt.
• Prosopis juliflora invasion: Banni grasslands, Kachchh, Gujarat.
• Living Planet Report 2024 (WWF): 73% average fall in vertebrate populations from 1970 to 2020. The worst region is Latin America and the Caribbean (95%) and the worst ecosystem is freshwater (85%).
• IPBES 2019: up to 1 million species face extinction. The most threatened group is amphibians (>40%).
• FAO 2025 review: 35.5% of 2,570 assessed marine stocks are overfished, but 77.2% of landings by volume come from sustainable stocks. The Mediterranean and Black Sea do worst.
• 99% of all species that ever lived are extinct, and an average species lasts 1–4 million years.
• The tropics have about 25% of the world's area, 75% of its people and 50% of its species.
• Trap: the Living Planet Report is WWF's report, not one by UNEP or IPBES. The Global Assessment is the IPBES report.

Mains Points

• Habitat loss as the main driver (GS-III): 75% of land and 66% of the sea have been altered, and over 85% of wetlands were lost between 1700 and 2000. In India, tropical forests are cleared for farms, mines and roads, and the remaining forest is broken into small patches. Answers should link this to land-use planning, eco-sensitive zones and wildlife corridors.
• Invasive species as a hidden driver: Lantana in tiger reserves, Prosopis in Banni and water hyacinth in wetlands cut native fodder, water and habitat. Invasives played a part in about 60% of recorded extinctions and cost over US$423 billion a year (IPBES 2023). Policy needs early detection, uprooting campaigns and controls on deliberate introductions.
• Overfishing and the blue economy: over a third of assessed marine stocks are overfished. India's staggered 61-day monsoon ban protects spawning on both coasts. It needs to be combined with limits on fishing effort, curbs on bottom trawling and support for fishers' incomes during the ban.
• Tropical paradox: half of all species live in the tropics alongside three-quarters of humanity, so poverty, population pressure and biodiversity loss feed each other. Latin America's 95% fall in the Living Planet Index shows this. Conservation must therefore go together with livelihoods.