Ecosystems &Biodiversity Measuring Species Diversity 1

Practical 4 Measuring and Comparing Species Diversity

Reading

Burgman M.A. & Lindenmayer D.B (1998) Conservation Biology for the Australian

Environment. Surrey Beatty & Sons. Chapter 2 What should be conserved ? sections 2.1-2.5.

Introduction

In an earlier practical we examined the difficulties faced when we try to place

individuals into separate taxa, or species, based on their morphology only. In this

practical we will look at an example, where we use “morphospecies” of moths collected

from three islands, to compare species diversity, and then make some recommendations

about conservation priorities based on the comparison. (What is a morphospecies?)

Comparing Species Diversity – Moths of SE Asia

Invertebrates are frequently used as biodiversity indicators because, taxonomically there

are many species, and ecologically because of the variety of habitats, niches and

strategies they utilize. Some groups, such as beetles, ants and moths and butterflies are

also relatively easy to distinguish into morhospecies using only external morphological

characteristics.

The Task

The moths in this practical come from the severely

degraded islands of Pulau Sipadan, Pulau Talang-

Talang and Pulau Redang. They have been brought to

you by Dr.Dale and you are going to use the differences

in species diversity as the rational to prioritize restoration

ecology programs for the islands. There are many Diversity Indices which can be

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calculated and compared – we will use Simpson’s Diversity Index. Read the

explanation at the end of this practical.

First, you must sort all the moths into “groups. Use characteristics which all the

moths have in common, but whose states vary. For example, relative antenna

length or ornimentation, wing colouration, wing markings, abdomen or thorax

size or shape might all be useful characters, but number of legs is not! Size is

also not a good characteristic to use (why?).

The “operational taxonomic units” or OTU’s, that you define (the groups) can

be considered as separate “species”. Give each species a unique name, for ease

of discussion (this is what taxonomists do).

First, pick a moth species, comapre all three islands at the same time, and

colour-in or mark all the individuals you think belong to the same group

(species). Then pick the next moth species and repeat the procedure, untill all

moths have been assigned to a group.

Second, count how many individuals belong to each species on each island and

enter the values into the table provided.

Then, calculate species diversity for each island using the Simpson index D.

You can do this by hand, or you can use one of the calculators on the web.

There are instructions at the end on the practical. If you use the online calculator

you can also easily calculate species richness and evenness.

Your Report

You should discuss the following points in an “essay style” report (about 600 words).

Give a title, brief introduction, and present a neat table giving the richness, eveness and

D values for the moth species, and your priority for conserving the three islands.

Reference your report .

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What are the basic ‘building blocks’ or “operational taxonomic units” of

‘biodiversity’ ? Explain.

Briefly explain what (1) species richness and (2) species evenness mean.

What was the order of the islands, from highest to lowest diversity?

How did you rank the islands for conservation? Did this follow the diversity values?

What other factors could you take into account when determining conservation

priority?

If we do not have the resources to protect all species, what criteria could we use to

decide where to focus our conservation efforts?

Due Date

Check the Assessment Details File for the date. This report is worth 10% of

your total mark.

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Table 1. Number of species and number of individuals of each species for three

Malaysian Islands. D = Simpson diversity index. P = priority ranking for restoration; 1

most urgent, 3=least urgent.

Species Pulau Sipadan Pulau Talang-

Talang

Pulau Redang

A 3 40 0

B 3 15 0

C 4 12 4

D 4 2 0

E 11 0 11

F 10 23 0

G 6 0 14

H 2 0 3

I 1 0 0

J 9 0 0

K 29 4 0

L 35 3 0

M 0 0 18

N 0 0 10

O 0 0 7

P 0 0 10

species richness 117 99 77

species evenness 12 9 8

Simpson Index (D) 1.35 5 0.67

Priority for Conservation 2 3 1

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Understanding Simpson’s Diversity Index

There are a number of good web sites which explain how to compare species diversity,

and some allow you to use their online calculator.

http://www.countrysideinfo.co.uk/simpsons.htm

http://www.umanitoba.ca/institutes/natural_resources/biodiversity/biodiversity.html

Simpson's Diversity Index is a measure of diversity. In ecology, it is often used to quantify the biodiversity of a habitat. It takes into account the number of species present, as well as the abundance of each species.

Biological Diversity - the great variety of life

Biological diversity can be quantified in many different ways. The two main factors taken into account when measuring diversity are richness and evenness. Richness is a measure of the number of different kinds of organisms present in a particular area. For example, species richness is the number of different species present. However, diversity depends not only on richness, but also on evenness. Evenness compares the similarity of the population size of each of the species present.

1. Richness

The number of species per sample is a measure of richness. The more species present in a sample, the 'richer' the sample.

Species richness as a measure on its own takes no account of the number of individuals of each species present. It gives as much weight to those species which have very few individuals as to those which have many individuals. Thus, one daisy has as much influence on the richness of an area as 1000 buttercups.

2. Evenness

Evenness is a measure of the relative abundance of the different species making up the richness of an area.

To give an example, we might have sampled two different fields for wildflowers. The sample from the first field consists of 300 daisies, 335 dandelions and 365 buttercups. The sample from the second field comprises 20 daisies, 49 dandelions and 931 buttercups (see the table below). Both samples have the same richness (3 species) and the same total number of individuals (1000). However, the first sample has more evenness than the second. This is because the total number of individuals in the sample

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is quite evenly distributed between the three species. In the second sample, most of the individuals are buttercups, with only a few daisies and dandelions present. Sample 2 is therefore considered to be less diverse than sample 1.

Numbers of individualsFlower Species Sample 1 Sample 2

Daisy 300 20Dandelion 335 49Buttercup 365 931

Total 1000 1000

A community dominated by one or two species is considered to be less diverse than one in which several different species have a similar abundance.

As species richness and evenness increase, so diversity increases. Simpson's Diversity Index is a measure of diversity which takes into account both richness and evenness.

As the species diversity increases, so does the value of Simpson’s Diversity Index D.

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Calculating Simpson’s Diversity Index online

Step 1. Log on to your computer and navigate to the following website –

http://www.umanitoba.ca/institutes/natural_resources/biodiversity/biodiversity.html

You should see the following screen.

Step 2. Click on the calculator shown

in Figure 1 on the screen, and the

following screen should appear.

Step 3. In the on-screen

data entry form, type in the

numer of individuals of

each moth species found on

the the first island. The

values must be separated by a space. This screen shows and example with seven

species; the first one has 10 individuals and the seventh species has 12 individuals.

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Step 4. Click the “calculate diversity” button, and a results box will appear like the one

below.

Step 5. In Table 1, record the Simpson’s D value (2 decimal places only), Species

Richness and Shannon’s Eveness value. From the above example D=0.82, Richness=7

and Evenness=0.92.

Step 6. Repeat the calculation for the other two islands.

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Calculating the Simpson Diversity Index by hand

This index is calculated as follows:

D = 1/pi2

where pi = the fractional abundance of the ith species on the island. For example if you

had a sample of two species with 5 individuals of one species and 8 individuals of the

other species (a total of 13 individuals)

D = 1 / (5/13)2 + (8/13)2)

= 1 / (0.38)2 + (0.62)2)

= 1/(0.52)

D = 1.92

so, as the value of D increases, so does the diversity.

Please note that you do not need to memorize how to do these calculations, but you

do need to remember that there are quantitative measures of species diversity.

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Calculating the Simpson diversity index – an example

Species Pulau Sipadan Pulau Talang-

Talang

Pulau Redang

1. 5 5

2. 8 7

3. 9 2

4. 6

total indiviuals 22 20

Simpson index (D) 2.8 3.6

Pulau Sipadan D = 1/((5/22)2 + (8/22)2 + (9/22)2)

= 1/(0.23)2 + (0.36)2 + (0.41)2)

= 1/(0.05 + 0.13 + 0.17)

= 1/0.35

D = 2.8

Pulau Talang-Talang D = 1/((5/20)2 + (7/20)2 + (2/20)2 + (6/20)2)

= 1/(0.25)2 + (0.35)2 + (0.10)2 + (0.30)2)

= 1/0.06 + 0.12 + 0.01 + 0.01)

= 1/0.28

D = 3.6

Therefore, as D = 3.6 is greater than D = 2.8 we can say that Pulau Talang-Talang has more moth diversity than Pulau Sipadan.

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Moths of SE Asia

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