A biodiversity survey is a way to measure the variety of living things in a small area, such as a schoolyard, garden, or park. In this project, students place a 1 m x 1 m quadrat on the ground and record every species they can identify inside it. The survey can include plants, insects, fungi, mosses, worms, fallen leaves, and other visible organisms.
This matters because biodiversity helps ecosystems stay healthy, stable, and able to recover from change.
After collecting counts, students organize the data in a table and calculate a diversity score using the Simpson Diversity Index. This index uses both species richness, the number of species present, and evenness, how balanced the species counts are. A plot with many species and similar numbers of each will have a higher diversity score than a plot dominated by one species.
Comparing quadrats from grass, garden beds, or shaded areas can reveal how habitat conditions affect biodiversity.
Key Facts
- A quadrat is a fixed sampling square, often 1 m x 1 m, used to count organisms in a defined area.
- Species richness = the number of different species found in the quadrat.
- N = total number of individual organisms counted across all species.
- n = number of individuals counted for one species.
- Simpson Diversity Index can be calculated as 1 - [sum n(n - 1)]/[N(N - 1)].
- A Simpson Diversity Index closer to 1 means higher biodiversity, while a value closer to 0 means lower biodiversity.
Vocabulary
- Biodiversity
- Biodiversity is the variety of living organisms in an area, including different species and their relative abundance.
- Quadrat
- A quadrat is a square frame or marked area used to sample organisms in a standard, repeatable way.
- Species richness
- Species richness is the number of different species found in a sample area.
- Evenness
- Evenness describes how similar the population sizes are among the species in a community.
- Simpson Diversity Index
- The Simpson Diversity Index is a number that estimates biodiversity by combining species richness and evenness.
Common Mistakes to Avoid
- Counting only the most obvious plants, insects, or fungi is wrong because small organisms can strongly affect the biodiversity score. Use a magnifying glass and check under leaves, along soil surfaces, and between grass blades.
- Changing the size of the quadrat during the survey is wrong because it makes samples unfair to compare. Keep each plot exactly 1 m x 1 m or clearly record the area used.
- Mixing species together in one category is wrong because the index depends on the count for each species. If exact identification is difficult, label organisms consistently as Species A, Species B, and so on.
- Using N as the number of species is wrong because N means the total number of individual organisms counted. Species richness is the number of different species, while N is the total of all individuals.
Practice Questions
- 1 A 1 m x 1 m quadrat contains 12 grass plants, 5 clover plants, 3 beetles, and 2 mushrooms. What are the species richness and total number of individuals N?
- 2 A quadrat has four species with counts 10, 8, 6, and 6. Calculate the Simpson Diversity Index using 1 - [sum n(n - 1)]/[N(N - 1)].
- 3 Two quadrats each have 30 total organisms. Quadrat A has 28 grass plants and 2 beetles. Quadrat B has 10 grass plants, 8 clover plants, 7 ants, and 5 moss patches. Which quadrat has higher biodiversity, and why?