Threats to ecosystems
Habitat destruction, genetic erosion, biodiversity loss, expanding agriculture, dams, waste and consumption.
Major threats to ecosystems
Habitat destruction and fragmentation is the biggest single cause of biodiversity loss. Forests are cleared for farms, mines, roads, dams and cities. Fragmentation breaks a large habitat into small patches; animals needing large areas (tigers, elephants, migratory birds) suffer most.
Biodiversity loss: NCERT-level biology lists the “evil quartet”: habitat loss and fragmentation, over-exploitation (over-hunting, over-fishing), invasion by alien species, and co-extinctions (when a host dies out, its specialised parasites or pollinators die too). Invasive species include water hyacinth (*Eichhornia*), *Lantana* and *Parthenium* in India. The Nile perch introduced into Lake Victoria in East Africa led to the loss of many native cichlid fish species.
Genetic erosion is the loss of genetic variety within a species. When farmers replace thousands of local crop varieties with a few high-yielding ones, the gene pool shrinks, and crops become more open to new pests and diseases.
Expanding agriculture clears forests and grasslands and drains wetlands; heavy fertiliser and pesticide use pollutes soil and water.
Dams flood forests and farmland, block fish migration, trap silt, and displace people. The Sardar Sarovar dam on the Narmada led to the Narmada Bachao Andolan, led by Medha Patkar. In Kerala, protests over a planned hydroelectric project in the Silent Valley led to the project being dropped and the area being declared a national park in 1984.
Waste and over-consumption: plastics, e-waste and chemicals pollute ecosystems; high consumption drives mining, logging and fishing beyond sustainable limits.
Key points
- Habitat loss = biggest cause of species loss.
- Evil quartet: habitat loss, over-exploitation, alien species, co-extinction.
- Genetic erosion = loss of variety within a species (often crops).
- Silent Valley (Kerala) → project dropped; national park 1984.
- Narmada Bachao Andolan → Sardar Sarovar dam.
Exam tips
Match examples to threats: Lantana → invasive species; dam → habitat flooding/displacement; HYVs → genetic erosion; parasite dying with host → co-extinction.
Common mistakes
- Confusing genetic erosion (within a species) with extinction (whole species gone).
- Thinking all introduced species are harmful; only those that spread and harm natives are invasive.
- Forgetting that dams harm rivers downstream too (less silt, blocked fish).