Diversity of Beans

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Name _____________________________________________
Measuring Species Diversity
Warm-up Questions
1. What are the benefits of biodiversity? List as many as you can.
2. How can diversity be measured? List as many things ecologists can measure about a community in an
ecosystem.
Ecologists are interested in diversity in an ecosystem because it is often a measure of environmental health and quality.
A diverse ecosystem has greater resilience to disturbance (why might this be?). A diverse ecosystem also tends to be
more productive, which is able to support even more organisms. Biologically diverse ecosystems also have many other
instrumental values that benefit us directly.
Diversity has two parts. One is species richness, which is simply the number of species found in an area. The other is
species evenness. Evenness tells us whether a particular ecosystem is numerically dominated by one species or whether
all of its species have similar abundances. For example, two forests might have the same number of species of trees, but
in one, it may be completely dominated by one type of tree with just one or two of the other species. These two
ecosystems will not function the same way.
Ecologists use indices so they can compare the overall diversity of ecosystems. There are two commonly used indices:
The Simpson’s Diversity Index (D) and Shannon’s Diversity Index (H). You will calculate D and H of four simulated
communities to compare the diversity and to compare the effectiveness of the indices.
Simpson’s Diversity Index (D)
The Simpson’s Diversity Index is calculated as follows.
 s

  ni ni  1 

D  1   i 1
 N ( N  1) 




Where:
N is the total number of individuals in a sample (sum of n).
ni is the number of individuals of a species i.
s is the total number of species (species richness).
Shannon’s Diversity Index (H)
The Shannon’s Diversity Index is calculated as follows:
s
H   pi ln( pi )
i 1
Where pi 
ni
N
Practice:
Suppose the data collected for an area is as follows:
Number of
Tree species
n(n-1)
individuals (ni)
Eastern Hemlock
5
White pine
3
Red oak
5
Yellow Birch
2
pi
ln(pi)
pi (ln(pi))
5 x (5-1) = 5 x 4 =
20
Total number of
individuals (N) =
∑n(n-1) =
∑pi(ln(pi))=
N(N-1) =
D=
H=
Materials:



Container of bean community
Paper plate
Calculator or computer
Procedure
1. Obtain a handful of the “bean community” on a paper plate. Determine the numbers of
different types of beans are present in your sample. Count the number of each bean
type and record your data on a data table you create in your notebook.
2. Return the beans back in the original container. Repeat the procedure with other “bean
communities”
3. Calculate the Simpson and Shannon Diversity Indices for each community.
Analysis
1. How did the species richness vary among your communities?
2. According to your data, how did dominance affect your Species Diversity Index value? (dominance is the degree
to which one or more species is more numerous than other species)
3. Based on the species diversity index you calculated, which community has the greatest species diversity? Which
one has the least?
4. Did the Simpson index and Shannon index result in the same ranking of diversity for the communities? How did
the indices differ in their results?
5. Which index do you prefer? Explain your reasoning.
6. Is the Shannon index or the Simpson sufficient for the ecologist when comparing diversity in ecosystems? What
other information might they need?
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