Genetic, species and ecological diversity

One word for all the variety of life

Walk through a forest, a pond and a paddy field in one day. You meet very different plants and animals. Even in one paddy field, the rice plants are not all the same. All this variety has a name. It is biodiversity.

The word was made popular by the sociobiologist Edward Wilson. He used it for the combined diversity at all the levels of biological organisation. NCERT describes three of them: genetic, species and ecological diversity.

Genetic diversity

A single species can show a lot of variety in its genes. This is genetic diversity. It is the variety inside one species.

• Rauwolfia vomitoria, a medicinal plant, grows in different Himalayan ranges. The plants of one range differ from those of another in the potency and the concentration of the active chemical, reserpine, which is used to treat high blood pressure. The genes of the plants differ.
• India has more than 50,000 genetically different strains of rice and about 1000 varieties of mango.

Species diversity

The variety at the level of the species is species diversity. It is the variety of species in a region.

NCERT gives this example. The Western Ghats have a greater diversity of amphibians than the Eastern Ghats. The number of species of frogs and their relatives is higher there.

Ecological diversity

India has deserts, rain forests, mangroves, coral reefs, wetlands, estuaries and alpine meadows. This is ecological diversity, which is the variety of ecosystems. NCERT compares it with a Scandinavian country such as Norway. India has a greater ecosystem diversity than Norway.

Notice the steps. Genes are inside a species. Species live in ecosystems. Each level has its own variety.

A way to measure species diversity

This part is not in the NEET syllabus, but A-Level and IB ask it.

Two meadows can have the same number of species, and still be very different. In one, the four species are nearly equal in number. In the other, one species fills the meadow and the other three are rare. The number of species is the richness. How evenly they are shared is the evenness.

Simpson's index of diversity counts both. If $n$ is the number of plants of one species and $N$ is the number of plants of all species, then

The index is between $0$ and $1$. A high value means high diversity.

You should find that making one species rule lowers the index, even though the richness stays four.

Try it in Python

The program gives the index of two meadows with four species each.

Practise with new numbers

Common mistakes

• Calling the number of strains of rice species diversity. All the strains are of one species, so this is genetic diversity.
• Writing that the Eastern Ghats have more amphibians. NCERT says that the Western Ghats have more.
• Thinking that more species always means a higher Simpson index. A meadow ruled by one species has a low index, even with many species.
• Forgetting to take the sum from 1. The sum alone is the chance of picking two plants of the same species.

Remember these

• 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. Western Ghats and Eastern Ghats amphibians.
• Ecological: among ecosystems. India compared with Norway.
• Simpson's index (not in the NEET syllabus): $D = 1 - \sum (n/N)^2$.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Reserpine from Rauwolfia vomitoria is more potent in plants of one Himalayan range than in another. Which level of diversity is this?

2. Name the three levels of biodiversity that NCERT describes.

3. A forest has 800 plants of one tree species and 10 plants of each of three other species. Does it have a high Simpson index? Give a reason.

4. Which has the greater ecological diversity, India or Norway? Give the reason NCERT gives.

5. A meadow has 50, 30, 15 and 5 plants of four species. What is its richness?

References

• NCERT (2023). Biology, Textbook for Class XII, chapter 13, Biodiversity and Conservation, section on the kinds of biodiversity.
• OpenStax Biology 2e (2018), chapter 47, Conservation Biology and Biodiversity, section on measuring biodiversity.
• Campbell Biology, 12th edition (2021), Pearson, chapter 56, Conservation Biology and Restoration Ecology, section on the three levels of biodiversity.