Kinds and Patterns of Biodiversity: Quick Revision

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

Levels

• Biodiversity: the variety of life at all levels. The word was made popular by Edward Wilson.
• Genetic: within a species. Rauwolfia vomitoria and reserpine. More than 50,000 strains of rice. About 1000 varieties of mango.
• Species: among the species of a region. Amphibians of the Western Ghats and the Eastern Ghats.
• Ecological: among ecosystems. India compared with Norway.
• Simpson's index (not in the NEET syllabus): $D = 1 - \sum (n/N)^2$. It counts richness and evenness.

How many, and where

• Described: about 1.5 million. Estimated: 20 to 50 million, and about 7 million by Robert May.
• Shares: animals more than 70 per cent, plants no more than 22 per cent, insects more than 70 per cent of the animals.
• Latitudinal gradient: high in the tropics, falling towards the poles. Birds: Colombia 1400, New York 105, Greenland 56.
• Three hypotheses: time for speciation, a less seasonal and predictable climate, more solar energy.

Species and area

• Equation: $\log S = \log C + Z \log A$, which is $S = C A^{Z}$. A rectangular hyperbola on plain scales.
• Z: 0.1 to 0.2 for regions. 0.6 to 1.2 for whole continents.
• Value of diversity: Tilman, steadier and higher productivity. Ehrlich, the rivet popper hypothesis.

A worked example

A region has $C = 6$ and $Z = 0.2$. How many species are in $1000\ \text{km}^2$?

1. Use $S = C A^{Z}$.
2. $S = 6 \times 1000^{0.2} = 6 \times 3.98 = 23.9$ species.

Practice with new numbers

A program to try

The program gives the species for three areas.

Mistakes to avoid

• Calling many strains of one crop species diversity. It is genetic diversity.
• Swapping the ranges of Z. Regions are 0.1 to 0.2. Continents are 0.6 to 1.2.
• Treating the hypotheses as facts. They are explanations that may work together.
• Writing that Tilman proposed the rivet popper idea. It was Ehrlich.

Check yourself

1. Name the three levels of biodiversity.

2. What is the slope of the species-area line for a region?

3. Which group has the most described species?

4. Who compared species to the rivets of an aeroplane wing?

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, chapters 54 and 56.