Biology
Sampling Diversity Field Exploration
Guiding Question:
1. What is biodiversity?
2. How do you measure the biodiversity of an ecosystem/habitat?
Objectives:
At the end of this exploration you will be able to:
 Describe how sampling may be used to answer scientific questions.
 Demonstrate topographical features using a crinkled up piece of paper.
 Discuss why representatives sampling is important and necessary to understand
biodiversity.
 Identify some of the sources of error in sampling and design ways to avoid them.
 Differentiate two methods of sampling and how they can be applied in different situations
 Discuss ways in which sampling is used to study the effects of climate change on an
ecosystem.
Background: Biological diversity - or biodiversity - is a term used to describe the variety of life on
Earth. It refers to the wide variety of ecosystems and living organisms: animals, plants, their habitats
and their genes. Scientists study groups of organisms to determine species abundance. They can use
this data on populations or communities to make comparisons with other places or to monitor
changes in ecosystems. Due to limitations of time, money, or personnel, scientists cannot count every
individual in most groups. To address this, scientists have devised a number of techniques that can
be used to obtain representative samples. These techniques are customized for different organisms,
situations, and purposes so that a true representative sample can be achieved.
Sampling is important for studying both populations and communities of organisms. The total number of
individuals is often the goal when sampling a population. A community’s biodiversity is often measured
with relative abundances of its species gathered through sampling. Relative abundances are an estimate of
the actual quantities of species relative to others in the same area. These are also important for studying
changes in abundances or differences between areas. Even large-scale ecosystem studies rarely include
every living organism within their borders, but instead focus on a clearly defined group of them.
Measuring Biodiversity
Sampling is one of the best ways scientists have to measure biodiversity. Biodiversity is usually measured
with two components: richness and evenness. Richness is the number of species in a particular area.
Evenness measures the similarity in the abundances of the species that are present. Low evenness means
that a community is dominated by just a few species, so it seems less diverse than the simple species count
would suggest. Evenness may have consequences for the ways species interact and for the stability and
productivity of a community.
Figure 1 illustrates how richness and evenness contribute to diversity. Three fields, shown as Field A,
Field B, and Field C, each have 16 individual mice. With five species, Field B has higher species richness
than Field A, which has two species. Field C also has five species, but greater evenness than does Field B,
which is largely dominated by two species.
Adapted from California Institute of Biodiversity
www.nextgenscienceinnovations.wordpress.com
Figure 1
Now look at the sample charts below. Comparing community 1 to community 2, make a claim as to the
richness and evenness of each community. My claim is: ____________________. Now compare
community three to the first two communities. Make a claim as to which of the three communities has the
greatest richness. My claim is: ________________________________.
Based on what you have learned so far make a claim as to which is of greater importance for ensuring
survival of a species, richness or evenness. What is the evidence for your claim?
Evenness by itself can be misleading. Think back to our unit on genetics. Describe the meaning of
“genetic diversity” and discuss what role genetic diversity may play in an ecosystem particularly in
regards to the notion of evenness.
Sample Communities
Community A
SPECIES
A
B
C
D
E
TOTAL
Community B
SPECIES
A
E
F
G
H
Total
NUMBER OF
INDIVIDUALS IN
SAMPLE
10
125
3
23
39
200
RELATIVE ABUNDANCE
RANK
10/200 = .050
125/200 = 0.625
3/200 = 0.015
23/200 = 0.115
39/200 = 0.195
4
1
5
3
2
NUMBER OF
INDIVIDUALS IN
SAMPLE
10
35
8
18
29
100
RELATIVE ABUNDANCE
RANK
10/100 = 0.10
35/100 – 0.35
8/100 = 0.08
18/100 = 0.18
29/100 = 0.29
4
1
5
3
2
Adapted from California Institute of Biodiversity
www.nextgenscienceinnovations.wordpress.com
Community C
SPECIES
A
B
C
D
E
F
G
H
I
J
TOTAL
NUMBER OF
INDIVIDUALS IN
SAMPLE
12
1
5
31
21
4
9
8
2
2
95
RELATIVE ABUNDANCE
RANK
12/95 = 0.126
1/95 = 0.011
5/95 = 0.053
31/95 = 0.326
21/95 = 0.221
4/95 = 0.042
9/95 = 0.095
8/95 = 0.084
2/95 = 0.021
2/95 = 0.021
3
10
6
1
2
7
4
5
8
9
In this exploration, you will learn two sampling methods (quadrats and transects) as a way of assessing an
area’s biodiversity in terms of richness and evenness. The exploration is split into three different sections.
First you will practice sampling methods in groups with mock organisms. Next you will choose a sampling
method based on the organism and area that you will sample outdoors. Finally, you will analyze you data
through bar graphs and rank-abundance curves as a way of representing the diversity within a community.
Part I: Sampling with mock organisms.
Materials needed: Large piece of butcher paper, string, small quadrant, “organisms.”
Question to ponder: If you were directed to count the number of blades of grass or number of ants at
Arroyo how would you accomplish this task?
Procedure:
1. Have one person crinkle the large piece of paper at your lab table. This is your habitat.
2. Randomly place your organism throughout your habitat. Use ALL the organisms in your bag.
3. As a class, identify each organism as organism A, organism B, organism C etc.
4. Your job is to use the equipment provided to count all the organisms in your habitat. However,
BEFORE you start be sure to come up with a protocol for collecting your data. Questions to
consider may include;
a. How will you be sure to get a representative sample? (It might be helpful to first think of
places in an ecosystem you DO NOT want to place your quadrant.)
b. How will you count an organism that is “half in and half out” of your quadrant?
c. How would data collection be different if you were using a transect?
d. What limitations are inherent in your sampling?
e. Will you count organisms above your sample area (Tree branches or creatures that fly)?
f. How would sampling animals be different than sampling plants?
5. After discussing and recording ALL these questions we will decide on a class protocol and begin
our sampling.
6. Create a data table to record the number of each type of critter. (See chart below for example)
7. Create a bar graph that accurately represents your sampling data.
8. Now create a pie chart to represent your data.
9. Finally, create an excel line graph for your results. The X axis is the rank of each species
in ascending order and the Y axis is the relative abundance. This graph is called the rank
abundance curve. By design the curve should decrease from left to right, since the more
common species puts them to the left.
Adapted from California Institute of Biodiversity
www.nextgenscienceinnovations.wordpress.com
10. You will now collect CLASS DATA. Create a data chart that shows the relative abundance of
each type of organism for the entire class.
11. Record and compare your results with results from the rest of the class. Create a bar graph to
represent the entire class biodiversity of organisms.
12. Transfer that data into a pie chart.
13. Create an excel line graph for class results. The X axis is the rank of each species in ascending
order and the Y axis is the relative abundance. This graph is called the rank abundance curve. By
design the curve should decrease from left to right, since the more common species puts them to
the left.
14. By looking at the graphs, you can quickly assess the richness and evenness of the communities.
The longer the curve stretches to the right, the more species the community contains, and the
greater its richness. The less peaked a graph is to the left, the less it is dominated by one or a few
species, and the greater its evenness.
Analysis and Questions and Discussion:



Which community has the most richness and evenness? What is your evidence?
If this was an actual outside habitat, what organisms were present within your habitat that you
could not see? What niche do these organisms have within your habitat?
Why do scientists sample if it will never reflect the real compositions of a given population?
Part II: Sampling in the Field.
Materials Needed: A PVC 1m quadrant, a string 25m long, various field guides, magnifying glass.
Procedure:
1. Decide on the type of sampling method you will use.
2. Decide on your sampling protocols.
3. All journal/scientific notebook entries must be in Grinnell format.
4. You may use your camera to photograph specimens for later identification BUT photographs
should not take the place of accurate sketches. Be sure to record the lat/long and elevation of your
sampling area.
5. Have FUN….and go sample!
Part III: Data Analysis.
If your sample included several plant or animal species:
 What kinds of species are common?
 Discuss your sample in terms of richness and evenness.
 What resources support them? What limiting factors keep their populations under control?
 Were you able to gather any information regarding the genetic diversity of your population? If not
how could that information be obtained?
 Did you observe any non-native species? If so, what problems do non-native species bring to an
ecosystem?
Adapted from California Institute of Biodiversity
www.nextgenscienceinnovations.wordpress.com