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.
Understanding Biodiversity Survey Project
Good fieldwork starts before any counting. Choose sites that answer a clear comparison, such as sunny lawn versus shaded lawn, or a garden bed versus an area beside a path. Keep the time of day, weather, observer effort, and sampling method as similar as possible.
These factors can change what is visible. A dry day may hide slugs and worms. Fresh mowing can remove flowers and make plant identification harder.
For a fair test, place several sampling squares in each habitat. Random placement reduces the temptation to choose a spot that looks especially interesting. Repeated samples give a better picture because one small patch can be unusual by chance.
Decide what counts as one individual before recording data. A separate dandelion plant is usually one individual, but a spreading grass or moss mat can be difficult to separate into individual plants. Write a rule and use it consistently in every plot.
For organisms that cannot be named, use careful labels such as small brown beetle type one and small brown beetle type two. A photo can help with later identification, but it is better to record an honest unknown category than to guess a species name. Do not count dead leaves as organisms, though they can be recorded as habitat evidence because they affect moisture, shelter, and food.
The diversity calculation gives more weight to common species than a simple species list does. First, find the total number of individuals in the plot. For each species, multiply its count by one less than its count.
Add those results for every species. Then divide that sum by the total number of individuals multiplied by one less than the total. Finally, subtract the result from one.
A plot containing only one very common plant produces a low result even if a few rare species occur there. The calculation is unreliable when very few individuals were counted, so note this limitation rather than treating every score as equally certain.
A score is evidence, not a final judgment about whether a place is good or bad. A low score may reflect trampling, mowing, dry soil, shade, pollution, or a recently disturbed area. It may simply reflect a habitat that naturally supports a few specialist species.
Compare the actual species table with the score. Two plots can have similar scores for different reasons. This kind of survey connects to real environmental work in parks, farms, construction sites, and restoration projects.
Good conclusions describe patterns carefully. State what was observed, identify possible causes, and explain which extra measurements, such as soil moisture, light level, or ground cover, would make the conclusion stronger.
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?