Part I: Random Sampling-Transect sampling
1) Tear a sheet of paper into 20 slips, each approximately 4cm x 4 cm.
2) Number 10 of the slips from 1 to 10 and put them in a beaker. Label the remaining 10 slips from A through J and put them in a
second beaker.
3) The grid shown to the right represents a meadow measuring
10 m on each side. Each grid segment is 1m x 1m. Each black
circle represents one sunflower plant.
4) Randomly remove one slip from each container. Write down
the number-letter combination and find the grid segment that
matches the combination. Count the number of sunflower
plants in that grid segment. Record this number on the data
table. Return each slip to its appropriate container.
5) Repeat step 5 until you have data for 10 different grid segments
(and the table is filled out). These 10 grid segments represent a
sample. Gathering data from a randomly selected sample of a
larger area is called sampling.
6) Find the total number of sunflower plants for the 10 segment
sample. This is an estimation based on a formula. Add all the
grid segment sunflowers together and divide by ten to get an
AVERAGE number of sunflower plants per grid segment.
Record this number in the table. Multiply the average number
of sunflower plants by 100 (this is the total number of grid
segments) to find the total number of plants in the meadow based on your sample. Record this number in your data table
7) Now count all the sunflower plants actually shown in the meadow. Record this number in the data table. Divide this figure by
100 to calculate the average number of sunflower plants per each grid.
Random Sampling Data
Grid Segment
(number-letter)
Number of
Sunflowers
Analysis: Answer the following questions in complete sentences.
1)
Compare the total number you got for sunflowers from the
SAMPLING to the ACTUAL count. How close are they?
2)
Why was the paper-slip method used to select the grid segments?
3)
Why do biologists use Sampling? Why can’t they just go into the
forest and count all the sunflower plants?
4)
Population Sampling is usually more effective when the population has
an even dispersion pattern. Clumped dispersion patterns are the least
effective. Explain why this would be the case.
Total Number of
Sunflowers
Average per grid
(divide total by 10)
Total number of plants in meadow
(multiply average by 100)
Total number of Sunflowers
(count by hand)
5)
Describe how you would use Sampling to determine the population of
dandelions in your yard.
6) Explain bow the math in this type of sampling can provide (if done properly)
relatively accurate data.
7) Which type of dispersion would be the most supportive in increasing accuracy
of this method?
8) Identify the specific type of organisms that this method is designed to estimate. Explain why.
7
3
5
11
8) In a forest that measures 5 miles by 5 miles, a sample was taken to count the number
of silver maple trees in the forest. The number of trees counted in the grid is shown
below. The grids where the survey was taken were chosen randomly. Determine how
many silver maple trees are in this forest using the random sampling technique. Show
your work!
9
Part II: Mark and Recapture: Be sure the bags are not destroyed and ALL the beans get back into the bags!!!!
1) You will receive a bag of beans that represents your population. Capture 20 “animals” by removing them from the bag.
2) Place a clear mark on them using the marker.
Number Recaptured
Trial Number
Number Captured
3) Return the marked “animals” to the paper bag. Shake
with mark
gently to distribute animals.
1
4) Without looking in the bag, select a small handful of
2
“animals” from the paper bag. This is the recapture
step. Record the number of “animals” captured as well as
3
the animals that were recaptured with a mark on the data
4
table.
5
5) Return the “animals” to the bag, shake the bag to
distribute the animals and repeat. Do 10 recaptures.
6
6) When the ten recaptures are completed, enter the total
7
number of captured animals and the total number
8
recaptured that have a mark.
9
Calculations: In order to estimate your population size, follow
10
this formula
TOTAL:
Estimate of Total Population =
(total number captured) x (number marked)
(total number recaptured with mark)
What is the estimation of your population? (Show your calculations below) Estimated Size ___________
Now, divide the beans and have each person count their handful. Record the actual number of beans here: Actual Size _________
BE CAREFUL THAT ALL THE BEANS STAY IN THE BAG WHEN DONE! CHECK FLOOR AND SINK PLEASE!
Analysis
1. Compare the actual size to the estimated size. Did you overestimate or underestimate?
2.
Do you think having more captures would make this method more or less accurate? Explain your answer.
3.
Given the following data, what would be the estimated size of a butterfly population in Thunderbird Park?
A biologist originally marked 40 butterflies in Thunderbird Park. Over a month long period butterfly traps caught 200
butterflies. Of those 200, 34 were found to have tags. Based on this information, what is the estimated population size of
the butterflies in Thunderbird Park?
4.
In what situations would mark & recapture work best. Explain.
5.
Sometimes students have numbers that are much higher or lower than the actual population. List 3 possible errors in this lab
that could cause this.
6. Identify 3 ways to make “estimates” more accurate.
7. What 2 dispersion methods of populations makes this method less accurate? Explain.
8. What is one way modern technologies have made both estimation numbers more effective and accurate?
9. How can capture and release methods cause problems with behavior studies in ecology?
10. How does the environments topography impact both methods of estimation? Identify 2 specific ways.