Diversity Result
Results are based on the species counts entered below.
Species Breakdown
| Species | Count | Proportion | n(n − 1) | p² | Share % |
|---|
Calculator Inputs
Enter species names and counts. You can also paste data as lines such as Oak, 24 or Pine 18.
Example Data Table
This table shows a small community sample for testing the calculator.
| Species | Count | Notes |
|---|---|---|
| Oak | 24 | Most common tree record. |
| Pine | 18 | Second largest count. |
| Fern | 12 | Common understory plant. |
| Moss | 9 | Lower but meaningful abundance. |
| Wildflower | 7 | Small flowering group. |
Formula Used
Simpson’s index measures how likely two randomly selected individuals belong to the same species.
Here, n is the count for one species. N is the total count for all species. The value D is often called dominance. Higher dominance means one or few species control the sample.
The calculator also shows the reciprocal index, written as 1 / D. It gives an effective diversity value. Richness counts how many species are present. Evenness compares the reciprocal value with richness.
How to Use This Calculator
Type each species name and its count. Add more rows when your sample has more species. You can also paste a list into the text box. Use one species per line. Separate the species name and count with a comma, tab, or space.
Choose how the table should be sorted. Select the number of decimal places. Press the calculate button. The result will appear above the form. Use the CSV button for spreadsheet work. Use the PDF button for reports, assignments, and field notes.
Understanding Simpson’s Index of Diversity
What the Index Shows
Simpson’s Index of Diversity is a useful ecological measure. It describes variety inside a community. It uses both richness and abundance. Richness means the number of species. Abundance means how many individuals each species has. A sample with many balanced species usually has high diversity. A sample ruled by one species usually has low diversity.
Why Counts Matter
Counts are the base of the calculation. Each species count is compared with the total count. This shows the weight of each species in the sample. A rare species adds richness. A common species strongly affects dominance. That is why the calculator displays proportions and squared proportions. These details make the result easier to audit.
Reading the Result
The dominance value D moves toward one when dominance is high. The diversity value 1 − D moves toward one when diversity is high. The reciprocal value becomes larger when the community has more effective variety. Evenness helps explain balance. A balanced sample has species with similar counts. An uneven sample has a few very large counts.
Field and Study Uses
This tool supports classroom tasks, field surveys, garden checks, and habitat reports. It can compare plots, ponds, forests, farms, or reef samples. Keep the sampling method consistent. Use the same area, season, and counting rule. This helps each comparison stay fair. Always review unusual counts before reporting.
Better Data Habits
Name species clearly. Avoid mixing groups at different taxonomic levels. Do not combine adults with seedlings unless your method says so. Record unknown species with temporary names. Update them later when identification improves. Export your table after every calculation. It creates a simple record for review.
FAQs
What is Simpson’s Index of Diversity?
It is an ecology measure that combines species richness and abundance. It shows how diverse a community is based on the chance that two selected individuals belong to different species.
What does a high value mean?
A high 1 − D value means the sample has stronger diversity. It usually means several species are present and their counts are more balanced.
What does D mean?
D is the dominance value. It estimates the chance that two randomly selected individuals belong to the same species. A higher D means greater dominance.
What is the reciprocal index?
The reciprocal index is 1 divided by D. It converts dominance into an easier diversity scale. Larger values suggest greater effective diversity.
Can I use zero counts?
Yes, but zero counts do not add abundance. The calculator can ignore them or keep them in the table for documentation.
How many species rows can I add?
You can add as many rows as needed. Very large lists are easier to enter by pasting data into the bulk data box.
Can this compare two habitats?
Yes. Calculate each habitat separately. Then compare diversity, dominance, richness, evenness, and total sample size for a fair interpretation.
Is the index enough for a full study?
It is useful, but not always enough. Strong studies also describe sampling method, season, location, effort, and identification limits.