Biology 440 – Wildlife Ecology
Name _______________________________
Exercise 3: Species Diversity Exercise (25 pts.)
Due: Beginning of class Thursday, 18 April 2002
Please show all work when answering the following questions on your attached answer sheet(s).
Background
A frequently expressed ecological principle states that species diversity increases with seral
advancement – until it plateaus (and perhaps declines slightly) at the climax community
(Figure 1).
9
Species Diversity
8
7
6
5
4
3
2
1
0
1
2
3
4
5
6
7
8
Age, yrs
Figure 1. Potential changes in species diversity as a community ages.
You have decided to test this principle by conducting field research. You carefully craft a
research design based on censusing mammals found in 3 different seral communities: 1) young
forest; 2) mid-successional forest; and 3) older growth forest.
A common measure of species diversity is the Shannon-Wiener Index (sometimes called the
Shannon-Weaver Index and you may even find it listed as the Shannon Index). An excellent
reference to check for this index is Zar (Zar, J. H. 1996. Biostatistical analysis, 3rd edition.
Prentice Hall, Upper Saddle River).
.
s
H '    ( p )(ln p )
i
i
i 1
where:
s = number of species
pi = proportion of total sample belonging to ith species
A measure of evenness also can be obtained with the Shannon-Wiener Index.
J '
H'
H
max
J’ = evenness measure (range 0 to 1)
H’ = Shannon-Wiener Index [range 0 to ln(s)]
H’max = maximum value of H’ = ln(s)
s = number of species
where:
If one wishes to test the null hypothesis (H0) that 2 samples come from communities that have
the same diversity, one can use a 2-sample t-test:
t
H '1  H ' 2
S H '1  H '2
S H '1  H '2  S 2 H '1  S 2 H '2
First, compute the variance for each sample/seral community. The variance of each H’ (S2H’) can
be calculated as:
S
2
H
f

where:
i
ln( f i )  (( f i ln( f i )) 2 / n)
n2
n = sample size = total number of species in each
community
fi = number of observations in category i = number of each
species (Note: pi = fi/n)
Compare computed t-test values with the critical value of the Student’s t distribution for infinite
degrees of freedom.
 = 0.05 (significance level)
critical t-value = 1.96
95% Confidence Intervals also can be computed as:
mean + critical t-value * standard deviation
= mean + 1.96 (SH)
The data collected are as follows:
Species
Peromyscus leucopus
Blarina brevicauda
Sorex cinereus
Glaucomys volans
Lynx canadensis
Mustela erminea
Martes americana
Didelphis virginiana
Rangifer spp.
Erethizon dorsatum
Young
53
2
17
0
1
26
2
38
2
15
Seral Community
Mid-Age
48
5
15
7
3
12
10
17
13
21
Old
82
19
4
26
9
12
18
3
13
25
Questions
1) Which community has the highest species richness? Provide numbers to support your answer.
Also show work on separate page(s).
2) Do the “Young” and “Old” seral communities differ in species diversity as determined by the
Shannon-Wiener Index? Provide numbers to support your answer. Also show work on
separate page(s).
3) Numerically, which community has the highest species evenness? Provide numbers to
support your answer. Also show work on separate page(s).
4) How similar are the seral communities? Provide numbers to support your answer. Also show
work on separate page(s).
5) What statistical procedure might you use to compare all 3 communities concurrently?