Transcript Species Diversity ConceptsAE

Calculating Diversity
Aquatic Ecology
Why quantify biodiversity?
• Initially thought that more diversity = more
stable ecosystem
• Now used to measure and track changes
How do we measure
biodiversity?
• Use functional categories
– Ecosystem, species, genetics
Describing Communities
• Two methods
– Describe physical attributes (e.g. age,
class, size class)
– Describe number of species and their
abundance
Biodiversity
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Diversity of living things
Term often misused and overused
Current focus in conservation studies
Includes interest in genetic, species and
ecosystem diversity
• We will use species as our focus but
concepts can be used for genetic and
ecosystem diversity as well.
Species Richness
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Number of species in a community
The simplest measure
Can count all spp only is few simple ecosystems
Does not consider number of individuals
Evenness
• Evenness is a measure of the relative abundance of the different species
making up the richness of an area.
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Numbers of individuals
Flower Species
Sample 1
Daisy
300
Dandelion
335
Buttercup
365
Total
1000
• What is the Richness?
• What is the Evenness?
Sample 2
20
49
931
1000
Species diversity
• Species richness not very informative
• Each community has 5 spp & 50 individuals
Comm
A
Comm
B
Spp
1
Spp
2
Spp
3
Spp
4
Spp
5
10
10
10
10
10
46
1
1
1
1
Diversity indices
• To get a better description of the
community we need to get a measure of spp
richness and evenness of their distribution
• We usually use an index to represent several
different measures
– E.g. stock markets, air pollution, etc.
Diversity indices
• Over 60 indices used in ecology
• Indices used to measure proportional
abundance
• Two major forms:
– Dominance indices (e.g. Simpson index)
– Information indices (e.g. Shannon Weiner
index)
Simpson Diversity Index (D)
– Simpson’s index considered a dominance index
because it weights towards the abundance of the
most common species.
– measures the probability two individuals
randomly selected from a sample will belong
to the same category
– For example, the probability of two trees, picked at
random from a tropical rainforest being of the
same species would be relatively low , whereas in
the boreal forest would be relatively high.
Simpson Diversity Index (D)
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I = (n1(n1 -1)/N(N-1))
Where:
Ds = 1-I
n1 = number of individuals of spp 1
N = Total number of spp in community
In this form as diversity increases index value
gets smaller
Simpson Diversity Index (D)
Mayflie stonefl Damself Midge Gilled Total
s
ies
lies
Snails
#
Species
56
48
12
6
((56*55)/(125*124))+
((48*47)/(125*124)) + ………….
….((3*2)/125*124)) = 0.35509
3
125
Simpson Diversity Index (D)
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Complimentary form = 1-I
= 1-0.35509 = 0.6449
Reciprocal 1/I = ds
1/0.35509 = 2.816
Questions?