Loss of biodiversity

Causes of biodiversity loss:

• Population growth has increased the use of natural resources. Tropical regions cover about one-fourth of the world's area but hold about three-fourths of its people. Over-exploitation and deforestation are rampant there, and tropical rain forests hold about 50 per cent of the earth's species.
• Natural calamities: earthquakes, floods, volcanic eruptions, forest fires and droughts damage plants and animals.
• Pollutants: pesticides, hydrocarbons and toxic heavy metals destroy weak and sensitive species.
• Exotic species: species that are not native to a habitat but are introduced into it have often caused extensive damage to the natural community.
• Poaching: tigers, elephants, rhinoceroses, crocodiles, minks and birds have been hunted for horns, tusks and hides, pushing some into the endangered category.

Classifying threatened species. The International Union for Conservation of Nature (IUCN) publishes the Red List of threatened species. The book gives three categories:

• Endangered: in danger of extinction.
• Vulnerable: likely to become endangered in the near future if the threats continue; their numbers have fallen greatly.
• Rare: very small world populations, confined to small areas or thinly spread.
• (Today's Red List groups critically endangered, endangered and vulnerable species as 'threatened'.)

Example (new): the water hyacinth, brought to India as a garden plant, now chokes many lakes and rivers, blocking sunlight and starving native water plants and fish of oxygen: an exotic species out of control.