TOC #
Population Sampling
Integrated Science 3
9/14
Name
Per
Introduction
A population is a group of organisms of the same species living in the same area. Populations have
unique characteristics not found in the individual members of the population. For this reason, they are of
considerable interest to scientists attempting to understand interactions in an environment.
When working with a population, often one of the first pieces of information an ecologist needs to
know is the actual size of the population. At first glance, this may seem a simple thing to determine. It
simply isn’t possible to examine or count every organism in an area. Sampling is a powerful tool that can
allow us to categorize an area, without counting everything. It would be time-consuming, frustrating, and
impossible to count every single snail on a beach or flower in the forest. Sampling is the process by which
organisms in small areas can be counted, or quantified, to estimate abundance over a larger area.
The small areas, or samples, must be representative of the larger area for these estimates to be
accurate. The more samples we look at, the more accurately we will be able to describe an area. This is why
replication, or repeatedly sampling an area, is important. Using representative sections of an area to
estimate the composition of a larger site can be a challenging concept.
This activity was developed to help introduce students to sampling and enable them to carry out
studies of species diversity and abundance. By finding a representative sample of a population, population
biologists can extrapolate to the larger population. For example, if in a sample 100 individuals are found in
a 1 m2 area and it is known the entire population covers a 50 m2 area, a simple ratio allows a biologist to
estimate the size of the total population to be 5000 individuals using the formula below:
Sampled Individuals
Total Population Size (x)
=
Sampled Area/Volume
Total Area/Volume

100individ.
x
, solve for x.
=
1sq.m.
50sq.m.
In this activity, you will be challenged to find an accurate size estimate for a “population” of beans in
a 600 ml beaker in a short amount of time using a simple sampling method.
Procedures
1. Obtain a beaker containing a bean “population” that occupies approximately 450 ml, and contains three
“variations” of beans - red, white and black. NOTE: The volume may vary so measure carefully so you
know the total volume of your bean population.
2. Place the “population” into the sampling bowl.
3. Collect a sample of the population by filling a 50 ml beaker to the 40 ml mark.
4. Count the number of beans of each color in one sample and record the sample size in data table. Note:
only count whole beans.
5. Return the sample to the sampling bowl and mix.
6. Repeat this sampling procedure 2 more times, recording your data in the data table each time.
7. Calculate the average of the three samples.
Sampling Data
Variation
Red Beans
White Beans
Sample 1
Sample 2
Sample 3
Mean Number of
Beans Sampled
Black Beans
Total Beans in
40 ml sample
Data Calculations
1. Using the mean number of beans sampled and the formula provided in the Introduction to calculate the
number of red beans, white beans, and black beans in the “population”, as well as the total
“population” of beans in the 600 ml beaker. Show your work in the space provided.
Population Calculations and Estimate
Show your work/ Formulas
Population estimate
Red Beans
White Beans
Black Beans
Total Beans
2. Get the actual values of each bean “variation” in the “population” from your teacher. Use these actual
values to calculate the percent error (difference) from your estimate.
Percent (%) Error =
Actual Values and % Error
Actual population
Actual Value - Estimated Value
Actual Value
´100
% Error (Show work, box answer)
Red Beans
White Beans
Black Beans
Total Beans
Discussion – Write or type your answers on a separate sheet of paper.
1. Describe what happened in the lab by discussing percent error values, which compare known values
with estimated values obtained through sampling.
2. Explain why the results occurred by summarizing the sampling process and discussing any sources of
error.
3. Discuss how the sampling process can be improved by offering suggestions for improvement, and
discuss how to further the process by suggesting other applications of the sampling process.