Threats to Biodiversity
NCERT Class 12 • Biology • Chapter "Biodiversity and Conservation" | NCERT Class 10 • Science • Chapter "Forest and Wildlife Resources"
Threats to Biodiversity
Species have always gone extinct, but the present rate is far above the natural background rate, and almost all of it traces back to human activity. Four causes account for most of the loss, and they are often summarised as the evil quartet.
The Four Main Causes
- Habitat loss and fragmentation is the single biggest cause, since a species with nowhere to live cannot survive however protected it is.
- Forest clearing for agriculture, mining, dams, roads and settlement has broken large habitats into small isolated patches.
- Fragmentation is damaging because animals that need a large territory cannot survive in a patch, and small isolated populations lose genetic diversity.
- Overexploitation means taking a resource faster than it can regenerate, as in overfishing and excessive hunting.
- Alien species invasion allows introduced species to multiply unchecked and displace native ones.
- Co extinction occurs when a species dies out and takes with it the species dependent on it, such as a specialised parasite or pollinator.
- Pollution and climate change now act as a further layer of pressure on top of these four.
Categories of Threatened Species
- Extinct means no individual survives anywhere, as with the dodo.
- Extinct in the wild means the species survives only in captivity or cultivation.
- Critically endangered means it faces an extremely high risk of extinction in the immediate future.
- Endangered means a very high risk, and vulnerable a high risk over a longer term.
- Rare species have small populations and endemic species occur only in one particular area.
- Indian examples of threatened wildlife include the great Indian bustard, the Ganges river dolphin, the snow leopard and the one horned rhinoceros.
- The red list is the international record that assigns each species to one of these categories.
| Cause | What Happens | Example |
|---|---|---|
| Habitat loss | Living space destroyed or divided | Forest cleared for farming |
| Overexploitation | Resource taken faster than it renews | Overfishing |
| Alien species | Introduced species displaces natives | Invasive weeds in lakes |
| Co extinction | Dependent species dies with its host | A specialised pollinator |
Endemic species — a species found naturally in only one particular geographical area and nowhere else.
Exam me kaise aata hai
- The biggest cause of biodiversity loss is — habitat loss
- A species found only in one area is called — endemic
- Loss of a dependent species along with its host is — co extinction
- The international record of threatened species is the — red list
UPSC/State PSC ke liye
- Fragmentation harms more than the area lost suggests, because edge effects and the isolation of small populations continue to degrade what remains.
- Endemic species are the most vulnerable, since a threat to their single habitat is a threat to the entire species at once.
Yahan confuse hote hain
✗ Extinct and extinct in the wild mean the same | Extinct in the wild survives in captivity | ✓
✗ Hunting is the main cause of extinction today | Habitat loss is the biggest cause | ✓
✗ Endemic species are always abundant | Endemic means restricted in range, which makes them vulnerable | ✓
Ek nazar me
- Habitat loss, overexploitation, alien species and co extinction are the main causes.
- Fragmentation isolates populations and reduces genetic diversity.
- Categories run from vulnerable to endangered, critically endangered and extinct.
- Endemic species are most at risk because their range is restricted.