Population Estimate
Background: The drawing represents a forest ecosystem. The forest floor is the habitat of the mouse-eared
toadstool. Your job is to determine the population density of this species by taking a sample census.
Process:
1. Trace the three shapes onto a sheet of paper and cut them out. Each plot covers 1 acre of forest floor.
2. Place the square plot on any location on the forest floor and count the toadstools completely or mostly covered
by the plot outline. Make a data chart like the one below and record the number in it.
3. Place the plot in a new spot on the forest floor and count again. Repeat until you have ten counts and record the
data in the chart each time.
4. Calculate the total count and record it in your data chart. Calculate the average population
Avg pop = pop count / 10
5. Repeat this procedure for the circular and rectangular plot.
6. Using a ruler, draw a straight line across the forest floor. This line is called a transect.
7. Place the rectangular plot lengthwise along the transect and count the toadstools as you did in step 2. Record the data in the chart.
8. Move the rectangular plot to a new location alon the transect, count the toadstools, and record the data. Work your way along the transect until you have counted 6 times.
9. Calculate the total and the average as you did before. Remember when you calculate the average this time to divide by 6 because you only counted 6 times.
Plot number |
Square |
Circle |
Rectangle |
Transect |
1 |
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2 |
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3 |
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4 |
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5 |
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6 |
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7 |
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8 |
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9 |
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10 |
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Total |
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Average |
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Questions:
1. Does this activity model a sample census or a true census?
2. Comment on the differences between the square, circular, and rectangular plots?
3. Each plot is 1 acre in size so the average you calculated is actually the average population density in toadstools/acre.
Pop density = pop count / plot area
4. The actual average population density is 2.5 toadstools per acre. Which trial was closest to this?
5. The forest is 49 acres. Calculate the estimated total toadstool population for each plot shape, including the transect method.
Est tot pop = avg pop density x 49 acres
6. Count the actual total population of mouse-eared toadstools. Which plot gave an estimated total population closest to the actual total population?
7. In question 5, you counted all the toadstools. Does this model a sample census or a true census?
8. How do you feel about the accuracy of your sample census compared to the true census?
9. Suggest a way to determine the population of: a) dandelions in the school yard. b) geese on the playing fields