Index of Diversity
Laura Armstrong
Teacher
Recall Questions
This topic requires prior knowledge of biodiversity. You can test your knowledge on this below.
What is biodiversity?
Biodiversity is the variety of living organisms in an ecosystem. It includes species diversity, genetic diversity, and habitat diversity.
What are the two main components of species diversity?
- Species richness
- Species evenness
What is species richness?
The number of different species within an area.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains index of diversity or read the full notes below. Once you've gone through the whole note, try out the practice questions!
What is Index Diversity?
The Index of Diversity (D) is a mathematical measure used to quantify biodiversity within a habitat.
It considers both species richness (number of species) and species evenness (the abundance of each species).
To calculate the index of diversity, you need to know:
The total number of all species.
The individual number of organisms in each species.
Formula for Index of Diversity
Where:
D = Index of Diversity.
N = Total number of organisms of all species.
n = Number of individuals of each species.
How to Calculate Index of Diversity Step-by-Step
Count the total number of organisms (N) in the community.
For each species, count the number of individuals (n).
Calculate n(n−1) for each species.
Find the sum ∑n(n−1) of all species.
Substitute into the formula and calculate D.
Interpretations:
Higher D = Greater biodiversity.
Lower D = Lower biodiversity (fewer species or dominance of one species).
Example Calculation
| Species | Number of Individuals (n) | n (n-1) |
| Species A | 10 | 90 |
| Species B | 5 | 20 |
| Species C | 3 | 6 |
| Total (N) | 18 | ∑ = 116 |
Interpretation: A higher value indicates greater species diversity, meaning the habitat is more stable and less likely to be affected by changes.
Key Terms
Biodiversity: Biodiversity is the variety of living organisms in an ecosystem. It includes species diversity, genetic diversity, and habitat diversity.
Species richness: The number of different species in an area.
Species evenness: The relative abundance of individuals within each species.
Index of Diversity (D): A numerical value that represents biodiversity within a community.
No answer provided.
Exam Tips
Don't confuse species richness with species diversity: Species richness is just the number of different species in an area, whereas species diversity also considers how evenly individuals are distributed.
Use the formula correctly: Ensure you correctly apply the Index of Diversity formula in calculations. Make sure to practice with me in the video question below!
No answer provided.
A student collected data on insect species in two different fields. The results are shown below:
| Species | Field A (Number of Individuals) | Field B (Number of Individuals) |
| Beetles | 20 | 15 |
| Butterflies | 10 | 5 |
| Grasshoppers | 5 | 3 |
| Spiders | 2 | 1 |
| Total (N) | 37 | 24 |
(a) Calculate the Index of Diversity (D) for Field A and Field B. (4 marks)
(b) Suggest a reason why Field A has a higher index of diversity than Field B. (2 marks)
(a)
Field A Calculation:
D= 37(36) / 492 = 1332 / 492 = 2.71
Field B Calculation:
D= 24(23) / 236 = 552 / 236 = 2.34
(b)
Field A has a higher Index of Diversity than Field B because it has more species and a greater species evenness.
Field B may have fewer species due to habitat destruction, pesticide use, or human activity such as deforestation.
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!