Teacher
Intructions and Materials
Names______________________________
______________________________
Estimating Population Size
Objective: You will be expected to estimate the size of a sample population using the mark-recapture technique. Be able to apply the technique to new population problems and compare the mark and recapture technique to other methods of population estimating.
1. If you were in charge of a team given the responsibility to determine the number of sunfish in Horseshoe Lake, discuss with your partner how would you accomplish this task and describe in detail below.
Technique 1: Sampling
A technique called sampling is sometimes used to estimate population size. In this procedure, the organisms in a few small areas are counted and projected to the entire area. For instance, if a biologist counts 10 squirrels living in a 200 square foot area, she could predict that there are 100 squirrels living in a 2000 square foot area.
2. A biologist collected 1 gallon of pond water and counted 50 paramecium. Based on the sampling technique, how many paramecium could be found in the pond if the pond were 20,000 gallons.
3. What are some problems with this technique? What could affect its accuracy?
Technique 2 - Mark and Recapture
In this procedure, biologists use traps to capture the animals alive and mark them in some way. The animals are returned unharmed to their environment. Over a long time period, the animals from the population are continued to be trapped and data is taken on how many are captured with tags. A mathematical formula is then used to estimate population size.
Procedure:
You will receive a bag that represents your population (beans, pennies, chips, beads)
Capture 10 “animals” by removing them randomly from the bag.
Place a mark on them using tape or string
Return the 10 marked “animals” to the container
With your eyes closed, select 15 “animals” from the contain one at a time. This is the recapture step. Record the number of “animals” recaptured that have a mark on the data table.
Return the “animals” to the bag and repeat. Do 10 recaptures.
When the ten recaptures are are completed, enter the total number captured on the data table
Also enter the total number of recaptured that have a mark
Data Table
|
Trial Number |
Number Captured |
Number Recaptured with mark |
|
1 |
15 |
|
|
2 |
15 |
|
|
3 |
15 |
|
|
4 |
15 |
|
|
5 |
15 |
|
|
6 |
15 |
|
|
7 |
15 |
|
|
8 |
15 |
|
|
9 |
15 |
|
|
10 |
15 |
|
|
Total: |
150 |
Calculations
In order to estimate your population size, follow this formula
Estimate of Total Population = (total number captured) x (number marked)
(total number recaptured with mark)
4. What is the estimation of your population? (Show your calculations below)
Estimated Size ___________
5. Use the code-name on your bag to check with the teacher about how many “animals” are really in your population.
Name on Bag ___________________________ Actual Size _____
Analysis
6. Compare the actual size to the estimated size. Did you overestimate or underestimate?
|
7. Repeat the experiment, this time add another 10 data fields to the ten trials you already have. Recalculate your estimate using the formula. (Show below)
What does this say about the number of trials that should be conducted in a real mark & recapture? |
|
8. Given the following data, what would be the estimated size of a butterfly population in Wilson Park.
A biologist originally marked 40 butterflies in Wilson park. Over a month long period butterfly traps caught 200 butterflies. Of those 200, 80 were found to have tags. Based on this information, what is the estimated population size of the butterflies in Wilson park?
9. In what situations would sampling work best for estimating population size, in what situations would mark & recapture work best. You’ll probably have to think about this one. Justify your answer.
*Remove all tags before returning your population!