Causes of biodiversity loss — the Evil Quartetजैव विविधता ह्रास के कारण — ‘दुष्ट चौकड़ी’

NCERT Section 13.1.4 · Class 12 Biology · Chapter 13 · interactive diagram

Parts and their functions

• Habitat loss and fragmentation (आवास क्षति व विखंडन) — The MOST important cause. Tropical rain forests once covered >14% of land, now ≤6%. The Amazon (‘lungs of the planet’) is cleared for soya beans and beef-cattle grasslands. Pollution degrades habitats; fragmentation hurts animals needing large territories and migratory animals.
• Over-exploitation (अति-दोहन) — When ‘need’ turns to ‘greed’. Steller’s sea cow and the passenger pigeon became extinct in the last 500 years due to over-exploitation; many marine fish are over-harvested today.
• Alien species invasions (विदेशी जातियों का आक्रमण) — Introduced species may turn invasive: Nile perch in Lake Victoria (east Africa) wiped out >200 cichlid fish species. Invasive weeds: carrot grass (Parthenium), Lantana, water hyacinth (Eichhornia). Illegal African catfish (Clarias gariepinus) threatens native catfishes.
• Co-extinctions (सह-विलुप्तता) — When a species dies out, species associated with it in an obligatory way also die out — a host fish and its unique parasites; a coevolved plant and its pollinator.

Original diagram drawn by Simple Learning Hub, based on NCERT Section 13.1.4. Report a mistake