Instructor’s copy
Lab Worksheet – You Can’t Catch Me
Hypothesis: Hypothesis will vary
Data and Observations: Data will vary but, since the fish aren’t reproducing, the number caught
each time should decrease.
Table 1.
Day
# of
fish
Table 2.
Day
# of
fish
Table 3.
Day
# of
fish
Table 4.
Day
# of
fish
Table 5.
Day
# of
fish
Table 6.
Day
# of
fish
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
Analysis Questions:
1. How might eagle predation affect the fish population over time? If the study time is limited to
the non-reproductive period of the fish, the number of fish should decrease.
2. What effect, if any, might a small scale decrease in the fish population have on the eagle
population? If it is small scale, the weaker one (or ones who don’t fish well) would die.
3. Ospreys and eagles compete for food. What effect, if any, might the competition have on the
eagle? More ospreys would eat the eagle’s food which would cause a decrease in the eagle
population since they would have less food.
4. Explain how a climate change might or might not indirectly affect the eagle population.
A climate change could change the amount of algae (and thus the oxygen available for the
fish) or freeze the lake. Both of these would decrease the fish population so the eagles would
not have enough food and their population would decrease.
5. What effect, if any, does an increase in the fish population have on the eagle population?
Since there would be more food, more eagles would survive to reproduce and the population
would increase.
6. How can a seasonal change affect the eagle population?
During the hot months, increases in weather might increase the water temperature and fish
would die from lack of oxygen. During the cold months, the lake might freeze so the eagles
could not fish. Both of these would decrease eagle populations due to a lack of food.
Students could also say that some weather conditions might cause the fish to breed and this
would increase the food source for the eagles.
7. What effect, if any, does the insecticide have on the fish population?
Based on the lab, the pesticide is not dangerous to the fish (although students should not be
marked wrong if they know that it could) so they might say that the pesticide has no effect
on the fish.
On the eagle population? The students who need enrichment should be held accountable for
knowing that if baby eagles don’t hatch, their population would decrease and the fish
population would then increase. Possibly give bonus points to the students requiring
enrichment for picking up on this relationship.
8. Can a pollutant, such as an insecticide, affect one population in an ecosystem and not another?
No, everything is dependent on everything else.
9. Explain how phosphate pollution can indirectly affect the eagle population.
Phosphates increase algal growth that decreases oxygen for the fish. The fish die and the
eagles are left without food.
10. How does an increase in the eagle population affect the fish population? How is this situation
similar to the competition from ospreys?
An increase in eagle population decreases the number of fish since more should get caught.
More predators cause a decrease in the prey, no matter what the predators are.
Checking your hypothesis:
Was your hypothesis supported by your data? Why or why not? May vary but should correctly
justify answer based on their own hypotheses.