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Measuring Biodiversity

Teacher Zonenature.ca/education

See the associated lesson plan atnature.ca/education/cls/lp/lpmb_e.cfm

Silk moth (Rothschildia orizaba).Michael Branstetter © Michael Branstetter

What Is Biodiversity?

• The term biodiversity comes from the words biological and diversity.

• It refers to the variety of life, and includes all living things (plants, animals and micro-organisms) and their unique characteristics.

Snail.Michael Branstetter © Michael Branstetter



• It can mean the variety of habitats, living communities and ecological processes in an ecosystem.

• It can mean the diversity of genetic characteristics within a species.

• It can mean the variety of species in a given area.


Why Is Biodiversity Important?

• Ecosystems depend on the combined contributions of the individual organisms within them. The loss of any species can prevent that ecosystem from operating the way it should.

• An ecosystem with a high level of biodiversity is more resistant to

environmental change.



• What does biodiversity mean to you?

• Let’s draw a mind map!


Biodiversity Index

• A biodiversity index is a way of measuring biodiversity.

• Scientists use different biodiversity indices to measure diversity,

and no single one will always be appropriate for the question being

posed.

• In fact, for some conservation questions, more than one measure

may have to be used.


Biodiversity Index

• Species Richness– The total number of species in

an area (add them up!)

• Species Evenness– How evenly the species are

represented in the area.– E.g., Do most of the individuals

belong to one species? Weevil (Rhodobaenus sp.). Michael Branstetter © Michael Branstetter


Species Richness

• The most common type of biodiversity index is species richness, which refers to the number of species in a particular place. This measure is commonly used because most people have an idea what “species” means.

• It is also commonly used because species keep their genes more or less to themselves, and to that extent have their own unique history.


Simpson’s Index

• Many diversity indices have been developed that combine different measures of biodiversity. One is called the Simpson’s Index.

• The Simpson’s Index includes BOTH species richness and species evenness in a single number.

Ocean sunfish (Mola mola).© iStockphoto.com/Todd Winner


How to Calculate Simpson’s Index

• D is the Simpson’s Index

• n is the total number of organisms of a particular species

• N is the total number of organisms of all species

• ∑ means “add up”!

D =∑ n(n - 1)

N(N - 1)


Let’s Try an Example

• You have studied a specific site, and have counted the individuals of five different species.

• n is the total number of organisms of a particular species.

Species A 12

Species B 3

Species C 7

Species D 4

Species E 9

n


Simpson’s Index

∑ n(n - 1) = 264

D =∑ n(n - 1)

N(N - 1)

Species A 12 11 132

Species B 3 2 6

Species C 7 6 42

Species D 4 3 12

Species E 9 8 72

∑ n(n - 1) 264

n - 1 n(n - 1)n


Simpson’s Index

D =∑ n(n - 1)

N(N - 1)

N - 1 = 34

N(N - 1) = 1190

N = total number of all individuals = 35

=264

N(N - 1)

D = 264

1190= 0.22184

This area would score 0.22184 on the Simpson’s Index. The scale ranges from 0–1, with 1 representing the lowest biodiversity. Therefore, the score for this area indicates a high level of biodiversity.


Biodiversity at Sites in Honduras The following calculations are based on sampling conducted in Honduras by Canadian Museum of Nature research scientist Bob Anderson.

Site N N(N - 1) ∑ n(n - 1) D SpeciesRichness

Cerro Montecristo 2996 7 120 892 1 600 002 0.2247 61

El Pital 2050 m 233 54 056 6856 0.1268 22

El Pital 2650 m 5411 29 273 510 12 873 694 0.4398 46

Cerro Puca 311 96 410 19 126 0.1984 27

Santa Barbara 839 703 082 55 514 0.0789 44


Biodiversity at Sites in Honduras

• Which site has the highest species richness?

• Which site is the most diverse according to the Simpson’s Index? (HINT: Has the lowest D).

• Do any sites have both a low Simpson’s Index and high species richness? Which one(s)?


Biodiversity and Conservation

• Which measure—species richness or species evenness— is more important to conservation?

• Should we incorporate both?

Canadian Museum of Nature scientist Bob Anderson identifying new species in the lab.John Longino © John Longino



• Why should we preserve biodiversity?

• What is conservation?

• What does it take to conserve areas?

• How is conservation related to biodiversity?

Pit viper (Cerrophidion godmani). José Monzon © José Monzon



• Some species are rare in nature, or in some areas. How is this important to conservation studies?

• Is there a chance that scientists might not even find the rare species?

• Are rare species more important to conserve than common ones?

Canadian Museum of Nature scientist Bob Anderson conducting a biodiversity assessment.Michael Branstetter © Michael Branstetter


measuring biodiversity page 1 teacher zone nature.ca/education see the associated lesson plan at...

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