The Loss of Biodiversity: Quick Revision

A brief note on The Loss of Biodiversity. Read it before a test. Try each question at the end before you open its answer.

How fast

• Mass extinctions: five in the past. The sixth is in progress, 100 to 1000 times faster than before humans, and caused by humans.
• Last 500 years: 784 extinct (338 vertebrates, 359 invertebrates, 87 plants). Dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller's sea cow (Russia), tigers of Bali, Java and the Caspian region.
• Threatened: 12 per cent of birds, 23 per cent of mammals, 32 per cent of amphibians, 31 per cent of gymnosperms.
• Effects: less plant production, less resistance to drought, more variation in the ecosystem.

The evil quartet

• Habitat loss and fragmentation: the most important cause. Rain forest from more than 14 per cent to about 6 per cent of the land. Amazon cleared for soya and cattle.
• Over-exploitation: Steller's sea cow, passenger pigeon, marine fish.
• Alien species invasions: Nile perch and more than 200 cichlid species of Lake Victoria. Carrot grass, Lantana, water hyacinth, Clarias gariepinus.
• Co-extinctions: a host and its parasites. A plant and its pollinator.

Why conserve

• Narrow utilitarian: direct uses. More than 25 per cent of drugs from plants.
• Broad utilitarian: services. About 20 per cent of the oxygen from the Amazon forest. Pollination. Beauty.
• Ethical: every species has a value of its own.
• Costanza: about 33 trillion US dollars a year, about 1.8 times the global product.

A worked example

A model class has 1000 species, and 12 per cent of them are threatened. How many are threatened?

1. Take 12 per cent of the number.
2. $0.12 \times 1000 = 120$ species.

Practice with new numbers

A program to try

The program works out the ratio of the services to the product.

Mistakes to avoid

• Counting six past mass extinctions. There were five, and the sixth is in progress.
• Mixing up the invaders. The Nile perch is in Lake Victoria. The African catfish is in our rivers.
• Calling pollination a narrow reason. It is a service, so it is a broad reason.
• Reading the share threatened as the share extinct.

Check yourself

1. Name the four causes of the loss of biodiversity.

2. Which cause is the most important?

3. Which group has the highest share of threatened species in NCERT?

4. Name the three kinds of reasons for conserving biodiversity.

Sources

• NCERT (2023). Biology, Textbook for Class XII, chapter 13.
• OpenStax Biology 2e (2018), chapter 47, Conservation Biology and Biodiversity.
• Campbell Biology, 12th edition (2021), Pearson, chapter 56.