Simpson Diversity Index Lab
Name
INTRODUCTION
Biodiversity is defined as the total number of species living in an ecosystem.
At present about 1.5 million species have been named, but this figure is not certain. It
is impossible to know how many species actually exist because we have not explored
every part of the biosphere yet. Most species are
also less than 1mm long so they are easily overlooked. Human actions such as
over exploitation, habitat destruction, introduction of alien species as well as pollution
have all contributed to a decrease in local and global biodiversity.
There are several reasons why we should want to maintain a high biodiversity
on Earth. High biodiversity is an indication of the health of an ecosystem and if an
ecosystem comes under stress from over exploitation or pollution, it will show low
diversity. Once diversity is lost from an ecosystem it can’t recover easily because species need to migrate back
in from neighboring ecosystems or if the organism has become extinct, it is lost forever.
In order to measure biodiversity, scientists must take two factors into consideration: species richness and
the size of the population of each species. To determine if a habitat is biologically diverse, researchers go into
the field to collect samples. Then, counting the number of groups and organisms and how many individuals
area in each group we can calculate the Simpson Diversity Index. With this number we can then determine if a
habitat is biologically diverse or not.
The Simpson’s Diversity Index (inverse) is calculated as follows:
2
A. Simpson Index = ∑(𝑃𝑖) “Sum of proportions, squared”
B.
C.
D.
E.
𝑛 2
Pi2 = (𝑁) “Proportion for each kind of bug collected, then squared”
n = number of individuals in one type, called an “Order”. (For example n=10 beetles)
N = Total number of all individuals collected in your samples
∑ = Greek letter sigma, it means to sum all the calculated proportions (Pi2). In other words, add up the
answers you calculated for each order of bugs found in the team’s sample.
Let’s try an example:
Organism Order
Cleopatra
(Beetles)
Lepidoptera
(Butterflies)
Hymenoptera
(Bee)
Odonota
(Dragon flies)
Hemiptera
(True Bugs)
Total (N)
n
10
N
33
2
33
5
33
1
33
15
33
33
Pi
10
= .303
33
2
= .061
33
5
= .152
33
1
= .030
33
15
= .455
33
(Sum) ∑ =
(Pi)2
0.092
0.004
0.023
0.0009
0.207
0.327
Simpson’s Diversity Index (SDI) sale starts with 0 as the best diversity and ends with 1 as the worst diversity.
Values nearer to zero show a highly diverse ecosystem and values nearer to one show a less diversity. The
LOWER the value, the GREATER the biodiversity! A SDI value less than 0.5 means that the environment has
healthy biodiversity, the lower the better.
PRE-LAB Practice: Data Analysis:
1. Each student group caught 50 insects in their sample. Use Simpson’s Diversity Index (SDI) to analyze
the following student data and determine which of the following 5 samples is most diverse. (The lowest
SDI value is the most diverse)
 Sample 1: 5 species, but there are 10 individuals in each species.
 Sample 2: 10 species with 5 individuals in the first species and 1 in each of the other species.
 Sample 3: 2 species, with 25 individuals in each species.
 Sample 4: 2 species, with 49 individuals in one and 1 individual in the other species.
 Sample 5: 10 species, with 41 individuals in one and 1 individual in the other 9 species.
Simpson Index Calculations ∑(𝑃𝑖)
𝟏𝟎 𝟐
𝟏𝟎 𝟐
𝟏𝟎 𝟐
2
SDI Value
𝟏𝟎 𝟐
(𝟓𝟎) + (𝟓𝟎) +(𝟓𝟎) +(𝟓𝟎) =
Sample #1
Sample #2
Sample #3
Sample #4
Sample #5
Mark your SDI values on the scale below (S1, S2, S3, S4, S5) to determine which sample shows the most
biodiversity.
Simpson Diversity Index (SDI Value)
0
0.2
0.4
0.6
0.8
1.0
Best
Very good
Good
Moderate
Poor
None
If all these samples were all collected in the same area we can calculate the biodiversity for the entire area by
averaging all five samples:
SDI Average:
Mark the SDI average on the scale above with the abbreviation: “Av”. What rating does the average for all
these samples have on the SDI scale?
Why is it important to calculate an average, if all the samples were collected in one area? How does an average
give a better understanding of biodiversity of the entire area being investigated?
Habitat Sampling: Collecting Invertebrates (Animals without backbones: insects, arthropods, spiders, etc)
1. The class will be investigating the question: How biologically diverse is the
habitat? Students will be able to answer this question by collecting samples using sweep nets in a
local habitat, such as a prairie, field, forest or school grounds.
2. Working in teams of 2-3, students will first record a hypothesis of where they think invertebrate
will be most biologically diverse. For example, “The most biodiversity will be found on the edge
of the prairie near the trees.”
3. Once students have recorded their hypotheses, each team will receive one sweep-net for collecting
samples, and a gallon Ziploc bag for storing the specimens. Use a Sharpie to label the bag with
your team member’s initials and date.
4. It’s important to try and collect a random sample, so when students are collecting they need to
choose a walking line to follow for the entire time of their sample collection. Try not to
deliberately catch any organisms, only sweep the net to randomly catch what is in front of you.
5. One member of the team uses the sweep net to catch living organisms by sweeping the net back and
forth through the plants and leaves of their habitat. They will sweep-net for one minute and then
stop to place their specimens in the Ziploc bags. The other team members will keep time and call
“stop” when sampling is finished.
6. Each team will collect 2, one-minute samples to be stored in their bag.
7. When all teams have collected their samples, all sample bags will be placed in a freezer for analysis
the next day in class.
In class data analysis and invertebrate identification:
1. Remove your sample bag form the freezer and empty the specimens on a dissection tray. Remove any plants,
leaves, twigs or debris and place in trash. Check for invertebrates before dumping, place any bugs on the
dissection tray.
2. If there are a large number of bugs, divide the sample among the team members and each person can work on part
of the sample.
3. Separate the bugs into groups and place similar invertebrates together.
4. Use the available identification keys to identify the invertebrate Orders for each group you create. For example, if
you have a pile of beetles all in one group, they are members of the Order: “Coleoptera”.
5. Use the data table provided to record the Orders your team identified, and the number of individuals for each
Order. Make sure to combine all team members’ samples together.
6. Once all invertebrates have been grouped and counted, calculate the Simpson Diversity Index for your sample.
7. Record your SDI value on the front board for your habitat. Record the SDI values of each team in the
data table for “class data”. If the class sampled in different habitats, record the class data for each
different habitat.
8. When everyone is finished with their samples and all SDI values have been recorded, clean your
dissection tray and place any remaining specimens in the trash and return the identification and any
other equipment.
Team Data Table
Invertebrate Order
n (# of individuals)
Class Data
1
2
3
4
5
6
7
8
9
10
Class Average
Pi = (n/N)
Pi2
(Sum)∑ =
Total (N)
Team
N (Total # in sample)
Record Class Average SDI Value on the scale below
SDI
NAME:___________________________________
period:_______
Lab Partners: ___________________________________&________________________________________
Hypothesis: ___________________________________________________________________________
_________________________________________________________________________________________
1.
Summarize the overall results for your sample and how the data from your sample supported or rejected your
team’s hypothesis.
2.
Did any Orders dominate in your sample? If so, explain what might cause this dominance (be sure to relate it
to environmental dominance).
3.
Human disturbances can cause changes in biodiversity. Based on class data, which area would you conclude
has most likely experienced some sort of human disturbance? Explain.
4.
Did your team find any invasive species, such as Asian or Japanese beetles? If so, how would your team’s
SDI change if you calculated it differently by separating the invasive species from the native species?
5.
The insects are indicators of how diverse the plant species are in the area the class sampled. Since all
organisms are connected, what level of biodiversity do you think this area has based on the plants?
6.
What could we do to improve the biodiversity of the habitat the class studied? What can the community to
help improve biodiversity?