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Special Topics in Ecology and Biodiversity
University of Malaya
2010
Biodiversity
DiversityBefore we tackle “biodiversity” let’s think
about the concept of diversityIn the simplest terms, diversity is
influenced by variation within and among groups
As will hopefully make sense in just a little while, diversity is influenced byThe type and amount of variationHow that variation is distributed
Below is a group of letters.What “variation” do you see here?
AAaa
Bbbbbbbb
cc
DDddd
Eeee
f
Variation Within a GroupDifferent letters (variation in type of letter)Variation within a type of letter
Capital vs. lower caseDifferent sizesDifferent colors
Different letters are represented different number of times
Variation Within a GroupThus, within a group
Different types (letters)Variation of characteristics within a particular
type.
What about variation between groups?
Which Group Contains More Variation?Group 1
ABCDE
Group 2AAAAA
Group 1 is more variableNo variation in Group 2
-all of the letters are exactly the same
More different types of letters in Group 1.
Variation Between GroupsGroups can differ in the number of types they containTherefore we think of a group containing more types
of things as being more variable than a group that contains fewer types.In this case we would consider groups with more
variation to be more diverse.
Which Group Contains More Variation?Group 1
BBBBB
Group 2BBBBB
Variation Between GroupsThe two groups share the same number of
types and number of representatives within a type
However, Group 2 has more variation among representatives within a type
In this case we would consider the group with more variation with a type to be more diverse.
Which group has more variation?Group 1
AAAAAA
Group 2AA
Variation Between GroupsThere is variation between groups in the
number of letters.Group 1 has more letters in it than Group 2
However, they are all the same letter all are the same format within a letter.
Thus, variation in numbers of things doesn’t appear to affect diversity.
Which group has more variation?Group 1
AAABBBCCC
Group 2AAAAAAABC
Group 1 is more variableGroup 1 and Group 2 have
- the same total number of letters- the same number of different types of letter
Therefore the variation among the two groups might be considered to be the same.
But almost all of the letters in Group 2 are A.- therefore we might consider that Group 1 is more diverse than group 2.
Variation Between GroupsSo differences in the number of individuals
within a type can influence diversity in some cases.
New TermDiversity can be influenced by the
“evenness” of the distribution of individuals among different types
Which Group is Most Even?Group 1
AAABBBCCCDDD
Group 2AAAABBCCCD
Factors That Influence DiversityNumber of different types of thingsVariation of characteristics within a typeEvenness of number of individuals across
different types of things
Which Group is More Diverse?Group 1
AABBCCDDEE
Group 2ABBCCCDEEF
This is a Tricky Question!!!!!Group 2 has more types of letters so we
might consider it to be more diverseGroup 1 contains a more even distribution
of letters within a type so we might consider it to be more diverse
Which group we consider to be the most diverse depends on how we rate the relative influence of number of types vs. evenness.The World is Complicated!!!!! (but luckily we
can use math to help us solve this problem)
Which Sample is More Diverse?
1. AaBbCcDd2. AAAAAAAA3. AABBCCDD4. AAaaBBbb5. AaBbCcDd
Rank according to number of types of letters1. AaBbCcDd - 4 letters2. AAAAAAAA- 1 letter3. AAAAABCD- 4 letters4. AAaaBBbb- 2 letters5. AaBbCcDd- 4 letters
1 = 3 = 5 > 4 > 2
Compare samples 1, 3, 5
1. AaBbCcDd 3. AAAAABCD Same richness but which is5. AABBCCDD more diverse?Sample 1.
Both capital and lower case lettersMore even (two copies of each letter)
Sample 3 Only capital lettersless even
Sample 5 Only capital lettersMore even
Can you come up with an equation that we can use to calculate “diversity” that we can use to compare samples?
What is “Biodiversity”?Biodiversity is a contraction of the two
words “biological diversity”.
Because biodiversity is such a broad, all encompassing concept there is not one well agreed on definition.
However, most definitions are similar.
BiodiversityA measure of the variety of organisms
within a local area or region, often including genetic variation, taxonomic uniqueness, and endemism.
- Ricklefs, The Economy of Nature
BiodiversityThe variety of organisms considered at all
levels from genetic variants belonging to the same species through arrays of species to arrays of genera, families, and still higher taxonomic levels; includes the variety of ecosystems, which comprise both the communities of organisms within a particular habitat and the physical conditions under which they live.E.O Wilson- The Diversity of Life
BiodiversityThe variability among living organisms
from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are a part; this includes diversity within species, between species, and of ecosystems."
Convention on Biological Diversity
Genetic DiversityMembers of the same population or species
can vary in which particular alleles they possess at a particular gene locus.
Population geneticists have a variety of techniques and metrics they use to measure the amount of genetic variation within and among populations.To learn more about this take an Evolution,
Population Genetics, or Conservation Biology course.
SpeciesSpecies are usually the focus of diversity
studies in ecology
Species- actually many definitions/species concepts
Biological Species Concept- group of potentially interbreeding
individuals that are reproductively isolated from other such groups
Biological Species ConceptTwo individuals are considered to be members
of the same biological species if they can potentially exchange genes.
Often difficult to apply this conceptAsexual speciesSpecies that are geographically isolated
How do we know whether a bird found in Europe can interbreed with a bird in North America
Ring species
But this is a conceptually pleasing definition of a species
Biological SpeciesSpecies are basic unit of biodiversity
Species may be subdivided into sub-species
Phenotypic Variation Within SpeciesVariation at the genetic, molecular,
physiological, morphological, or behavioral levels.Conservation biologists can be especially
concerned about genetic variationGenetic variation influences the potential for
natural selection
Species DiversitySpecies diversity is a characteristic of a
communityTwo components of species diversity
The number of species in a communitySpecies richness
evenness
Diversity IndicesEcologists have developed several metrics
to quantify species diversityThese indices differ in how they weight the
two critical components of species diversitySpecies richnessEvenness
Species RichnessSpecies richness simply counts the number
of species found in a community
Diversity Example Species number of individuals 1 10 2 20 3 15
Species RichnessBecause there are three species found in
this community
Species Richness = 3
Species RichnessStrengths
We are often interested in knowing about the numbers of species in a community
Easy number to calculateAll we have to do is count the number of species
This is an easily understandable metricWeakness
Ignores the evenness component of diversity
Which is more diverse?Try to make up a formula that will calculate
a number to use to measure diversity?
Remember- diversity increases as richness and evenness increases
Shannon Diversity Index s H = - ∑ (pi * ln pi) i=1
where:H = the Shannon diversity indexPi = proportion of the population made up of species iS = numbers of species in sample
Let’s Try an Example Species # individuals
1 102 203 30
Shannon Index ExampleFirst calculate the pi for each of the S
species in the sample (S = 3 species)
1. determine the total number of individuals sampled in the community
# sp.1 = 10 # sp.2 = 20
# sp.3 = 30
Total # = 60 ind
Shannon Index Example2. For each of the S species
pi = # ind species i/total # ind
pi
sp 1- 10/60 = 0.17 sp 2- 20/60 = 0.33
sp 3- 30/60 = 0.50
Shannon Index ExampleNext calculate H
s H = - ∑ (pi * ln pi)
i=1
Shannon Index Example
H =- ((0.17*ln0.17 + 0.33*ln0.33 + 0.50*ln0.50))
H = - (0.17*-1.77 + 0.33*-1.11 + 0.50*-0.69)
H = - (-0.30 – 0.37 – 0.35)
H = - (-1.01)
H = 1.01
Shannon IndexThe Shannon Index was designed such that
H gets larger when there are more speciesNot surprising because H should get larger when
there are more species in the sample (larger S)
Shannon IndexThe Shannon Index was designed such that
H gets larger when evenness is greater
Shannon IndexPi
0.1ln pi
-2.30259Pi * ln pi
-0.23026
0.2 -1.60944 -0.32189
0.3 -1.20397 -0.36119
0.4 -0.91629 -0.36652
0.5 -0.69315 -0.34657
0.6 -0.51083 -0.3065
0.7 -0.35667 -0.24967
0.8 -0.22314 -0.17851
0.9 -0.10536 -0.09482
1 0 0
Shannon IndexThe value of H gets larger whe
There are more speciesThere is greater evenness
Thus, diversity of a community increases as the value of H increases
Shannon IndexAdvantages
The value of H changes in a way that is consistent with our view of how changing species richness and evenness should affect species diversity
It is relatively easy to calculateDisadvantage
The value of H doesn’t have a direct biological meaningWhat do you know if someone tells you that H =
2.3?Useful only for comparison
Pielou’s Evenness Index - based on Shannon Index
E = H/Hmax
H is the value of the Shannon Diversity Index for a particular population
Hmax is the maximum value for the Shannon Diversity Index in a population with the same number of species and total number of individuals sampled
Hmax
For a particular community the maximum value of H would occur if all species were equally abundant.
After doing the algebra, Hmax can be calculated as follow-
Hmax = lnS
Evenness Index ExampleE = H/Hmax
E = 1.01/ln3
E = 1.01/1.098
E = 0.919
Simpson’s Index
D = ∑ pi2
D measures the probability that two randomly selected individuals in a population belong to the same species
D ranges from 0 – 1D will be largest when all individuals in a population are members of the same population
Thus, as D gets larger diversity decreases
Example D = ∑ pi
2
D = (0.172 + 0.332 + 0.502)
D = (0.0289 + 0.109 + 0.25)
D = 0.388
Simpson’s Index of DiversitySimpson's index of diversity = 1 - D
The probability that two randomly selected individuals in a community belong to different species.
Thus, as the Simpson’s Index of Diversity increases the species diversity of the population increases.
Simpson’s Index of DiversitySimpson's index of diversity = 1 - D
The probability that two randomly selected individuals in a community belong to different species.
Thus, as the Simpson’s Index of Diversity increases the species diversity of the population increases.
Diversity IndicesShannon Index is more sensitive to
changes in species richness
Simpson’s Index is more sensitive to changes in evenness
Diversity IndicesWhich diversity index should you choose to
use?It might depend on whether you were more
concerned about rare species E.g., changes in the number of rare species has a
much greater effect on Shannon’s Index than it does on the Simpson Index
Many researchers choose to use a number of different diversity indices because they provide different information.
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