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Let's Calculate Biodiversity: Try These Data

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A group of tiny mussels attached to a biofilm disc, viewed under a microscope
A biofilm community from Baltimore's Inner Harbor.

In this activity, you will calculate measures of biodiversity, as discussed on the How To Calculate Biodiversity page. The data comes from one of the many datasets gathered during our study of biofilm formation in Baltimore's Inner Harbor.

Before you get started, here is a quick review of the biodiversity formulas:

  • Species Richness (S): the number of different species found on the disc
  • Pi: the number of a given species divided by the total number of organisms observed
    When you compute the probability for each species, use decimal percent (e.g., 0.25; not 25% or 1/4)
  • Simpson's Index: D = sum(Pi2)
  • Simpson's Index of Diversity: 1 - D
  • Simpson's Reciprocal Index: 1/D
  • Shannon-Weiner Index (H): H = -sum(Pilog[Pi])
    While you may use any base, the natural log is commonly used
  • Evenness (E): E = H/log(S)

For more about each of these formulas, visit the How to Calculate Biodiversity page.


Assignment: Calculating Species Richness and Simpson's Index Using Three Species

Using the species counts, fill out the following tables to calculate the species richness and the three biodiversity indices develop by Simpson.

After you enter your answer(s) for each step, press the "Check Answer: button. You can use the "Clear Answer" button to clear the answer(s) for any part of this activity.

Tiny aquatic worms, called whip mud worms, on a biofilm disc
A biofilm community from Baltimore's Inner Harbor.

1. Calculate species richness (S)

Fill in the box with your answer and press the "check answer" button.


Assignment: Calculating Species Richness and Simpson's Index Using Three Species

Using the species counts, fill out the following tables to calculate the species richness and the three biodiversity indices develop by Simpson.

After you enter your answer(s) for each step, press the "Check Answer: button. You can use the "Clear Answer" button to clear the answer(s) for any part of this activity.

1. Calculate species richness (S)

Fill in the box with your answer and press the "check answer" button.

Species Name# FoundPiPi2 MeasureValue
Whip Mud Worm8  S  
Mussels20  D 
Barnacles15  1 - D 
Totals43  1/D 

2. Calculate the Simpson Index (D) value

First, calculate the percent of each species identified in the sample. Place your answers in the Pi column (up to 3 decimal places). Do not calculate the sum of the Pi column (it will be done for you).

Species Name# FoundPiPi2 MeasureValue
Whip Mud Worm8 S
Mussels20 D 
Barnacles15 1 - D 
Totals43 
  

3. Calculate the square of each percent for each species.

Place your answers in the Pi2 column (up to 3 decimal places). Do not calculate the sum of the Pi2 column (it will be done for you).

Species Name# FoundPiPi2 MeasureValue
Whip Mud Worm8S
Mussels20D 
Barnacles151 - D 
Totals431/D 

The sum of the Pi2 values is really Simpson's Index (D). All that is left is for you to calculate the Simpson's Index of Diversity (1-D) and Reciprocal Index (1/D).

4. Calculate the Simpson's Index of Diversity (1-D) and Reciprocal Index (1/D).

Place your answers in the boxes for 1-D and 1/D (up to 3 decimal places).

Species Name# FoundPiPi2 MeasureValue
Whip Mud Worm8S
Mussels20D
Barnacles151 - D
Totals431/D

5. The final results look like this!

Click here to see the final results
Species Name# FoundPiPi2 MeasureValue
Whip Mud Worm80.1860.035 S3
Mussels200.4650.216 D0.373
Barnacles150.3490.122 1-D0.627
Totals431.0000.373 1/D2.681

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