Name _____________________________ Class _________________ Date _________________
That’s Amazing! Worksheet
Poison Frogs: Leaf Litter
with Dr. Michael Heithaus
Problem
Do poison dart frogs have anything to worry about? They are not in danger from
predators, but their populations are decreasing even in areas that are protected.
One hypothesis is that a decrease in leaf litter is causing the decline.
A decrease in leaf litter could lead to problems for frogs that live there because the
frogs need the moist habitats under the leaves to prevent their skin from drying out
and also use it as a place to reproduce.
Use the data that Steven and Mike collected to investigate this problem.
INVESTIGATION
To test the hypothesis that the amount leaf litter influences the abundance of
strawberry poison dart frogs, Steven created an experiment with three treatments
and 10 replicates of each treatment (so he had 30 plots in all). In all 30 plots,
Steven removed all the leaves from the ground, then he put the same amount of
leaf litter back into 10 plots, put no leaves back into 10 plots, and put twice as
many leaves as he removed back into 10 plots. After six months he came back to
see how many strawberry poison dart frogs there were in each plot.
1. Identify the control, independent variable, and dependent variable in Steven’s
experiment.
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2. Predict which of the three treatments will have the most and the fewest
strawberry poison dart frogs, assuming that leaf litter is important for
maintaining healthy populations of frogs.
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© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
That’s Amazing! Worksheet
1
Biology in the 21st Century
Section 3: Scientific Thinking and Processes
Name _____________________________ Class _________________ Date _________________
Poison Frogs: Leaf Litter continued
3. Data Analysis Complete Table 1 by calculating the average for
each treatment.
Table 1. Counts of frogs in different treatments of the leaf litter experiment.
Strawberry poison dart frogs
Replicate
No change
Leaves added
Leaves removed
1
5
10
2
2
4
15
0
3
7
3
1
4
4
18
1
5
5
15
2
6
6
8
9
7
16
12
0
8
6
14
3
9
8
17
0
10
6
11
2
Average
4. Data Analysis Draw a graph of the average counts of frogs in each of
the treatments.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
That’s Amazing! Worksheet
2
Biology in the 21st Century
Section 3: Scientific Thinking and Processes
Name _____________________________ Class _________________ Date _________________
Poison Frogs: Leaf Litter continued
CONCLUSION
5. Are changes in the amount of leaf litter a potential threat to strawberry poison
dart frogs? Support your answer and speculate on why this relationship occurs.
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6. Use the data for strawberry poison dart frogs in Table 1 to argue why it is
important to have multiple replicates of each experimental treatment.
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7. Extension What other studies might you conduct to investigate the impact of
leaf litter on populations of strawberry poison dart frogs?
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8. Extension What other factors that affect populations of strawberry poison dart
frogs could you study? How would you test your ideas?
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© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
That’s Amazing! Worksheet
3
Biology in the 21st Century
Section 3: Scientific Thinking and Processes