Transcript diversity slides

Measuring Diversity
Community A
Community B
Species diversity
• Often defined as a combination of the
number of species and their relative
abundance.
Diversity Divisions
• Alpha diversity refers to species richness
• Beta diversity describes the degree of
change in species richness from one habitat
to another.
• Gamma diversity relates to the total
regional species diversity that results from
the number of habitats present.
Diversity Divisions
• Alpha diversity refers to species richness
• Beta diversity describes the degree of
change in species richness from one habitat
to another ~ habitat patchiness
• Gamma diversity relates to the total
regional species diversity that results from
the number of habitats present.
Diversity Divisions
• Alpha diversity refers to species richness
• Beta diversity describes the degree of
change in species richness from one habitat
to another.
• Gamma diversity relates to the total
regional species diversity that results from
the number of habitats present.
Number of species
• Species richness
– Method – simply count the number of different
species you observe, regardless of abundance.
– Therefore, if a species occurs 1 or 100 times, its
richness is still 1.
Community A
Community B
Relative Abundance
• Species evenness = assesses the relative
numerical importance of each species
– the contribution of each species to the total
number of individuals in the community
Relative Abundance
• Method – count up the number of each
individual observed or collected and divide
by the total number observed or collected.
– RA = n/N
• the percent contribution made by each
species to the community
Community A
Community B
Simpson Index
• A measurement that accounts for the
richness and percent of each species from a
biodiversity sample within a community.
Simpson Index
• This index assumes that the proportion of
individuals in an area indicates their
importance to diversity.
• So, it measures not only diversity but
dominance as well.
Simpson Index
• Can actually refer to any one of 3 closely
related indices.
– Simpson's Index (D) measures the probability
that two individuals randomly selected from a
sample will belong to the same species
• Ranges between 0 and 1, the lower the value, the
greater the sample diversity
Simpson Index
• Simpson's Index of Diversity 1 – D
measures the probability that two
individuals randomly selected from a
sample will belong to the same species
– Ranges between 0 and 1, the greater the value,
the greater the sample diversity
Simpson Index
•
Simpson's Reciprocal Index 1 / D
provides the number of equally common
categories (e.g., species) that will produce
the observed Simpson's index.
–
Ranges between 0 and total # species
collected, the higher the value, the greater the
diversity
Species
Number (n)
n(n-1)
Woodrush
2
2
Holly (seedlings)
8
56
Bramble
1
0
Yorkshire Fog
1
0
Sedge
3
6
Total (N)
15
64
D = 0.3 (Simpson's Index)
OR:
Simpson's Index of Diversity 1 - D = 0.7
Simpson's Reciprocal Index 1 / D = 3.3
Simpson Index
• Simpson's Index gives more weight to the
more abundant species in a sample. The
addition of rare species to a sample causes
only small changes in the value of D
Species
Number (n)
n(n-1)
Woodrush
2
2
Holly (seedlings)
8
56
Bramble
1
0
Yorkshire Fog
1
0
Sedge
3
6
Total (N)
15
64
Shannon-Wiener index
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•
•
Also been called the Shannon index and
the Shannon-Weaver index.
Used to compare diversity, doesn’t give a
measure of dominance.
Similar to Simpson's Index, this measure
takes into account species richness and
proportion of each species within a
community.
H' = -Σ{ pi*ln(pi)}
where H = Information content of sample, Index of species
diversity, or Degree of Uncertainty, s = Number of species pi =
Proportion of total sample belonging to ith species
IN EXCEL = LN (pi) will give you the natural log
Species
Name
# Found
Species
Species
Species
Species
Species
Totals
1
2
3
4
5
40
40
40
40
40
200
Species
Name
# Found
Species
Species
Species
Species
Species
Totals
1
2
3
4
5
1
1
196
1
1
200
Pi 2
Pi
0.2
0.2
0.2
0.2
0.2
1
Pi
0.005
0.005
0.98
0.005
0.005
1
0.04
0.04
0.04
0.04
0.04
Pi 2
0
0
0.961
0
0
Pi ln[Pi ]
-0.322
-0.322
-0.322
-0.322
-0.322
Pi ln[Pi ]
-0.026
-0.026
-0.02
-0.026
-0.026
Measure
S
D
1-D
1/D
H
Measure
S
D
1-D
1/D
H
Value
5
0.2
0.8
5
1.609
Value
5
0.96
0.04
1.041
0.126
Shannon-Wiener index
• Unlike the Simpson index, H is interpreted
that the higher the score the more diverse.
What does diversity tell us?
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Comparison purposes
Recovery purposes
Community interaction
Community summary