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.