How to measure Biodiversity

7/29/2019 How to measure Biodiversity

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Measurements of

Ecological Diversity

How to measureDiversity in an ecological system

Laila, Vimal, & Rozie


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Diversity-Stability Hypothesis

McArthur (1955)

WHY ?
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Ecologists describe distribution of diversity on a spatial scale

in three classifications.

The diversity of organisms within aselected habitat or sample.

Index of the rate of increase of alpha

as new habitats are sampled.

The full species diversity/ species richness.

Alpha, Beta, and Gamma diversity measures are Scale Dependent.

Whats that mean?


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Ecologist one studies:

One acre of land

and calls this

one habitatmeasuring alpha

diversity.

Ecologist two studies microbial organisms,

therefore one acre of land would containan infinite amount of microhabitats underhis consideration. The one acre of land would

be measuring Gamma Diversity.
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What are the properties of the community thatcan be measured to indicate its alpha diversity?

The total number of species within the sample

although relative frequencies are unknown.

Richness and Balance

Refer to Figure 2.1 pg 31


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There an infinite number of different mathematical

functions to describe diversity indices by encapsulatingdifferent aspects of the balance between richness and balance.
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Each of the Indices mention require the calculation

of a Population Proportion Pi

S: the total number of species in the sample.Ni : the number of individuals in the ith species.Total number of individuals in a sample may be

calculated as: NThe proportion made up by species i(denoted pi) is given

Pi: NiN

Procedure: Convert the count for each species in a sampleto a proportion of the total number of individuals

within the sample.


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The Simpson Index

measures the probability that two consecutive randomsamples from a population will find the same species.

The probability that a random sample from a populationwill pick out a given species is assumed to be equal tothat species contribution to the whole population. Pi = Ni/N

The probability of sampling species i in two consecutivesamples is found as follows: p(sampling species i twice) = pi* pi

A more realistic model equation:

P(sampling species I twice) = Ni(Ni-1)/ N(N-1)

The probability of sampling any species twice in twoconsecutive samples can be found as: P(sampling any species twice)= (pi*pi)


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Interpreting the Simpson Index

If there is only one species, pi = 1, hence (pi*pi)=1. This is called the zero diversity condition.

As the number of species tends to infinity, (pi*pi)

tends to zero, which is the high diversity condition. Simpsons index is usually altered to reverse the

above arrangement.

D= 1-(pi*pi)

So this equation calculate the probability of two consecutivesamples will be of different species.

D is the standard symbol for the Simpson index.


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The Shannon Index

Most commonly used diversity index.

H= -pi x log(pi)

H: Symbol for Shannon Index.

Negative sign (-) makes sure f value is received.

Community with one species (Pi = 1.0), diversity is zero.

If a community with S # of species, maximum possible value of theShannon index is log(S)- this occurs when all species occur at

equal frequency.


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For ecological studies, logarithms base 10 are used.

Converting between logarithms of different bases:

Loga(X)= Logb(X)/Logb(a)

Combine + = H(base2)= [- pi x log10(pi)]/ log10(2) =

3.3219 x H(base 10)


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Let us calculate the ratio of calculated diversity with maximum possible diversityfor the number of species found.

E= H/Hmax = [-pi x log(pi)]/ log(S)

Does not matter what sort of logarithm is used.

Reflects evenness of species distribution within sample.

An equitability near zero shows the community to be dominated by one species.

An equitability near 1.0 indicates an equal balance between all species.


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Both the indices mentioned do not come with estimates of

variability.Why would a scientist be interested in estimates of variability?

Jack-Knifing is an extension of the resampling process,

performed by a computer using the completed final dataset.

It obtains estimates of the variability withinparameter estimates in a wide range of

settings, including diversity indices.
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Successional changes in communitystructure, such as a bare habitat

where colonization starts with a few

colonist species, followed by a

gradual increase in numbers as

new species arrive.

First year: low-species diversity

281 individuals, 280 one species.

Simpson diversity: 0.007

Shannon diversity: 0.034


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First graphed: unclear trend, no

stabilizing of values due to dominance

of one species.

The species richness diversity indexshows a clear pattern: increases

consistently every year.


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Interest: the effects of

increased atmospheric

pollution on the growth of

coarse grasses.

Problem: high levels of

nitrogen deposits due to

ammonia release.

Effect:stimulates coarsegrasses in preference to

the rich community of low-

growing, less vigorous herbs.

Five experimental plots:

Brachypodium pinnatum was

present, not dominant.

* different concentrations of

nitrogen, phosphorus, &potassium fertilizers.

* increase in biomass,

decrease in number of

species.

Data summarized using

Shannon index.
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Ecological Conclusion:Brachypodium pinnatum is able to flourish on high levels of

nitrogen & low levels of phosphorus. The coarse grass wasable to use its height to shade out other species therefore

1. Reducing Biodiversity

2. Reducing conservation value of habitat.
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Used when the randomness of sampling is not guaranteed.

HB= [ ln(N!)-ln(ni!) ] / N HB: Brillouin IndexN: Total number of individuals in the sample

ni: number of individuals of species

Unlike the Shannon & the Simpson indices, this index varies with sample size

as well as with the relative proportions of species. Why?


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Only calculates the proportion of the most common species in

d= Nmax/ N

D= [N-(ni2)1/2] / N-N1/2


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Homework

What are the three distributions of diversity

on a spatial scale within ecology?

What does the Simpson index measure?

Calculate the species richness, Simpson

Index and Shannons Index (base 10)? Please show all your calculation


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Raw Data

Achillea millefolia 0

Arrhenatherium elatius 0

Calluna vulgaris 95

Deschampsia flexuosa 0

Festuca rubra 10

Heracleum sphondylium 0

Trifolium repenas 0

Vicia sativa 0

Data for Homework problem 3

Documents

How to measure Biodiversity