Biodiversity Tests Using the
Simpson’s Diversity Index
Reference: Molnar, W. Laboratory Investigations for AP Environmental Science. 2005
Introduction:
Ecologists often use biodiversity measurements to determine the health of an
ecosystem. A declining biodiversity indicates a declining ecosystem and can indicate that the
ecosystem is or was undergoing some environmental stress.
There are a great number of ways biodiversity is calculated. One of the most common
and easiest methods is the Simpson’s Diversity Index. This method calculates not only the
number of species represented in a given habitat but also how well each species is
represented; therefore, the method takes into account much more than just species richness.
The Simpson’s Diversity value (D) ranges from no diversity at 0.0 to a maximum diversity at
1.0. These values have no real meaning themselves but merely are used as a means of
comparison for different habitats or the same habitat at different times. A large D value
indicates that if you were to go out and collect two organisms from a habitat the odds would
be that the two organisms would be different species.
Example Calculation of Simpson’s Diversity Index:
s
ni
i=1
N
D = 1 –  
Where
s = the number of morphotypes (species)
i = a given morphotype
ni = the number of individuals in morphotype i
N = the total number of individuals collected (for all morphotypes)
Say:
Community A
Species 1
1000
Species 2
100
Species 3
100
Community B
Species 1 400
Species 2 400
Species 3 400
For Community A:
For Community B:
s=3
n1 = 1000
n2 = 100
n3 = 100
N = 1200
DA = 1 – [(1000/1200)2 + (100/1200)2
+ (100/1200)2]
s=3
n1 = 400
n2 = 400
n3 = 400
N = 1200
DB = 1 - [(400/1200)2 + (400/1200)2
+ (400/1200)2]
DA = 0.292
DB = 0.667
Prelab Question:
Use the Simpson’s diversity index to determine which of the following three communities of
100 individuals is most diverse. Community 1 contains 10 species, with 91 individuals of the
first species, and 1 individual of each of the remaining species. Community 2 contains only 5
species, with 20 individuals of each. Community 3 contains 10 species, with 18 individuals
from 2 of the species and 8 individuals from the remaining 8 species.
Sticky Trap Setting Procedure:
In the lab:
Using a Sharpie put your name and location at the top of the 3 sticky traps given to you. The
top part is the yellow strip at the top with no backing. If the sticky traps are not hole punched,
hole punch the middle top portion of the sticky trap so you can hang the trap with string if you
choose to do so.
In the field:
1. Go to your location site and place the sticky traps in order within your given location.
Place your sticky trap on the ground or secure the trap onto a stick, a wall, a fence, a plant, a
rock, etc., 0 to 3 feet from the ground. After setting each trap, remove the wax paper from the
trap. Return to the site after at least 45 minutes to collect the traps.
Bait Card Setting Procedure:
In the lab:
Using a pencil this time put your name and location on the lined side of the 4 index cards
given to you. Also label two of the cards “sugar” and two “tuna”.
In the field:
Scoop a small amount of tuna onto the cards labeled “tuna” (be sure to get the oil on the card
also). You should have a sample about the size of a quarter. Use the cotton swab to transfer a
dollop of corn syrup onto the cards labeled “sugar”. This sample should be about the size of a
nickel. Place the four bait cards (two sugar and two tuna) 3 to 5 feet apart from each other in
your location. If wind is a problem, place a small stone or stick on the card to weigh it down.
Return to the site after at least 20 minutes (longer if time allows).
Bait Card Collection Procedure:
Once 20 minutes has elapsed return to the bait cards to observe any activity that has occurred.
Collect the bait cards and observe the number of different morphotypes present on each card.
Compare your morphotypes with those found in the same location so you and another group
in the same location don’t count the same morphotype twice.
Sticky Trap Collection Procedure:
Once 45 minutes has elapsed return to the sticky traps to observe any activity that has
occurred. Collect the traps and observe the number of different morphotypes present on each
trap. Compare your morphotypes with those found in the same location so you and another
group in the same location don’t count the same morphotype twice.
Species found by you from both the sticky traps and bait cards.
Individual Data
Description of Morphotype
ID of Species?
Number of that
species represented
Species found by all the members sampling at your location from both the sticky traps and
bait cards.
Location Data
Description of Morphotype
ID of Species?
Number of that
species represented
What was your location?
Refer to your location data and calculate your location’s Simpson’s Diversity Index.