Over-exploitation = using a resource faster than it can regenerate. Historical extinctions due to over-exploitation: Dodo (Raphus cucullatus): flightless bird of Mauritius — hunted to extinction by Dutch sailors and invasive rats by 1681. Steller's sea cow (Hydrodamalis gigas): large marine mammal — hunted to extinction for meat/oil within 27 years of discovery (1768). Passenger pigeon (Ectopistes migratorius): most abundant bird in North America — hunted in billions, last one died in Cincinnati Zoo 1914. Cheetah: extinct in India due to hunting and habitat loss. Dodo, great auk, and quagga (striped zebra) all extinct from over-exploitation.

Water hyacinth (Eichhornia crassipes) = 'Terror of Bengal'. Native of Amazon basin, South America. Introduced to India in 19th century. Problems: covers water surface → blocks sunlight → kills aquatic plants. Depletes dissolved oxygen → kills fish (oxygen sag). Interferes with boat navigation, fishing, irrigation. Causes water loss through evapotranspiration. Forms dense mats → habitat for mosquitoes → malaria risk. Control: biological control using weevils (Neochetina eichhorniae), manual removal, herbicides. Lantana camara: another invasive plant in Indian forests — similar problems.

Steller's sea cow (Hydrodamalis gigas) was a massive marine mammal (8-9 metres long, ~10 tonnes) that fed on kelp in shallow waters around Commander Islands (Bering Sea). Discovered by Georg Steller in 1741. By the time it was discovered by Europeans, population was already small (~2000 animals). Russian fur traders hunted it for: meat (nutritious, tasty), fat (oil for lamps), leather (boat covers). Within just 27 years of European discovery (by 1768), the species was completely extinct. Example of how rapidly over-exploitation can eliminate a species.

Passenger pigeon (Ectopistes migratorius): once the most abundant bird in North America (estimated 3-5 billion individuals). Flocks darkened the sky for days. Hunted commercially from 1800s: shot, netted, trapped in millions. Meat sold cheaply for food. By 1900: fewer than a dozen known wild birds. Last known individual 'Martha' died in Cincinnati Zoo, September 1, 1914. Cause of extinction: synergistic effect of over-hunting + habitat destruction (forests cleared for agriculture). Shows how species can go from billions to zero within decades with human pressure.

Amazon rainforest: largest tropical rainforest (5.5 million km²), spans 9 countries (mostly Brazil). Contains 10% of all species on Earth. Deforestation causes: (1) Agriculture: soybean cultivation (Brazil is world's largest soybean exporter), cattle ranching, palm oil. (2) Logging: timber extraction. (3) Mining, roads, settlements. Rate: historically ~17,000 km² yr⁻¹ at peak. Consequences: species extinction, climate change (Amazon is a major carbon sink), altered rainfall patterns (evapotranspiration drives regional rainfall). 'Point of no return': scientists warn that 20-25% deforestation may permanently transform Amazon to savanna.

Species-level: Protect highly threatened species (tigers, rhinos, elephants) through reserves, captive breeding, anti-poaching. Ecosystem-level: protect ecosystems (national parks, marine protected areas) — more efficient than species-by-species. Biosphere reserves, Ramsar sites (wetlands of international importance). India: Project Tiger (1973), Project Elephant, Crocodile conservation, Sea turtle conservation. International: CITES (Convention on International Trade in Endangered Species) — regulates trade in threatened species. CBD (Convention on Biological Diversity). IUCN — maintains Red List. WWF, WCS — NGOs supporting conservation.

Mutualism: both species benefit. Obligate mutualism: both species completely dependent on each other → if one goes extinct, other follows (co-extinction). Examples: Fig trees and fig wasps — each fig species has its own fig wasp species. 700+ fig species = 700+ fig wasp species. If fig species lost → fig wasp also lost. Yucca plant and yucca moth. Certain orchid species and their specific pollinators. Lichens: fungus + algae/cyanobacteria symbiosis — technically both form a composite organism. Many parasites are highly specific to their hosts → host extinction = parasite extinction. Coral reefs: coral bleaching → loss of zooxanthellae → coral death → hundreds of fish, invertebrate species lose habitat.

Sacred groves (Dev van/Van): patches of forest protected by local community based on religious/traditional beliefs. Complete prohibition on felling, hunting, collection in the core area. Examples: Meghalaya (Khasi and Jaintia hills) — some of the most species-rich forest fragments in South Asia. Western Ghats. Rajasthan: 'Orans' or 'Dev vans'. Uttarakhand: 'Dev vans'. Tamil Nadu: 'Kovil kaadukal'. Sacred groves have preserved many rare endemic species that have disappeared from surrounding areas. Represent community-based conservation — complementary to government-protected areas. Threatened by modernisation, migration, and loss of traditional values.