Measuring Biodiversity
Silk moth (Rothschildia orizaba).
Michael Branstetter © Michael Branstetter
See the associated lesson plan at
nature.ca/education/cls/lp/lpmb_e.cfm
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What Is Biodiversity?
•
The term biodiversity comes from
the words biological and diversity.
•
It refers to the variety of life, and
includes all living things (plants,
animals and micro-organisms) and
their unique characteristics.
Snail.
Michael Branstetter © Michael Branstetter
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What Is Biodiversity?
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It can mean the variety of habitats, living communities and ecological
processes in an ecosystem.
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It can mean the diversity of genetic characteristics within a species.
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It can mean the variety of species in a given area.
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Why Is Biodiversity Important?
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Ecosystems depend on the combined contributions of the individual
organisms within them. The loss of any species can prevent that
ecosystem from operating the way it should.
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An ecosystem with a high level of biodiversity is more resistant to
environmental change.
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What Is Biodiversity?
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What does biodiversity mean to you?
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Let’s draw a mind map!
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Biodiversity Index
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A biodiversity index is a way of measuring biodiversity.
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Scientists use different biodiversity indices to measure diversity,
and no single one will always be appropriate for the question being
posed.
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In fact, for some conservation questions, more than one measure
may have to be used.
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Biodiversity Index
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Species Richness
– The total number of species in
an area (add them up!)
•
Species Evenness
– How evenly the species are
represented in the area.
– E.g., Do most of the individuals
belong to one species?
Weevil (Rhodobaenus sp.).
Michael Branstetter © Michael Branstetter
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Species Richness
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The most common type of biodiversity index is species richness, which refers to
the number of species in a particular place. This measure is commonly used
because most people have an idea what “species” means.
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It is also commonly used because species keep their genes more or less to
themselves, and to that extent have their own unique history.
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Simpson’s Index
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Many diversity indices have been
developed that combine different
measures of biodiversity. One is
called the Simpson’s Index.
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The Simpson’s Index includes
BOTH species richness and species
evenness in a single number.
Ocean sunfish (Mola mola).
© iStockphoto.com/Todd Winner
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How to Calculate
Simpson’s Index
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D is the Simpson’s Index
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n is the total number of organisms
of a particular species
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N is the total number of organisms
of all species
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∑ means “add up”!
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∑ n(n - 1)
D =
N(N - 1)
Let’s Try an Example
n
•
•
You have studied a specific site, and
have counted the individuals of five
different species.
n is the total number of organisms
of a particular species.
Species A
12
Species B
3
Species C
7
Species D
4
Species E
9
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Simpson’s Index
n
D=
∑ n(n - 1)
N(N - 1)
∑ n(n - 1) = 264
n-1
n(n - 1)
Species A
12
11
132
Species B
3
2
6
Species C
7
6
42
Species D
4
3
12
Species E
9
8
72
∑ n(n - 1)
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264
Simpson’s Index
D =
∑ n(n - 1)
N(N - 1)
=
264
N(N - 1)
N = total number of all individuals = 35
N - 1 = 34
N(N - 1) = 1190
D
=
264
1190
= 0.22184
This area would score 0.22184 on the Simpson’s Index. The scale
ranges from 0–1, with 1 representing the lowest biodiversity. Therefore,
the score for this area indicates a high level of biodiversity.
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Biodiversity at Sites in Honduras
The following calculations are based on sampling conducted in Honduras
by Canadian Museum of Nature research scientist Bob Anderson.
N
N(N - 1)
∑ n(n - 1)
2996
7 120 892
El Pital 2050 m
233
El Pital 2650 m
Site
D
Species
Richness
1 600 002
0.2247
61
54 056
6856
0.1268
22
5411
29 273 510
12 873 694
0.4398
46
Cerro Puca
311
96 410
19 126
0.1984
27
Santa Barbara
839
703 082
55 514
0.0789
44
Cerro Montecristo
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Biodiversity at Sites in Honduras
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Which site has the highest species richness?
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Which site is the most diverse according to the Simpson’s Index? (HINT: Has the
lowest D).
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Do any sites have both a low Simpson’s Index and high species richness?
Which one(s)?
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Biodiversity and Conservation
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Which measure—species richness
or species evenness— is more
important to conservation?
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Should we incorporate both?
Canadian Museum of Nature scientist Bob
Anderson identifying new species in the lab.
John Longino © John Longino
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Biodiversity and Conservation
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Why should we preserve
biodiversity?
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What is conservation?
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What does it take to conserve
areas?
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How is conservation related to
biodiversity?
Pit viper (Cerrophidion godmani).
José Monzon © José Monzon
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Biodiversity and Conservation
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Some species are rare in nature, or
in some areas. How is this important
to conservation studies?
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Is there a chance that scientists
might not even find the rare
species?
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Are rare species more important to
conserve than common ones?
Canadian Museum of Nature scientist
Bob Anderson conducting a biodiversity
assessment.
Michael Branstetter © Michael Branstetter
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