Activity 85 – Answer Key
Pre-Reading Questions:
1. What is a population?
A population is a group of organisms in a given place at a given time.
2. What do you think it means for a population to run out of space? _______________________________
3. What does carrying capacity mean to you in terms of ecology? _________________________________
Reading Questions:
1. Stopping to think #1- Refer to the graph on page E-73. Zebra mussels filter plankton out of the
water to eat. What do you think is happening to the quantity of plankton at:
a. Point A? Explain your reasoning.
At Point A, the quantity of plankton is increasing, therefore the number of mussels is
going up also. __________________________________________________________________________
b. What is happening to the quantity of plankton at point B? Explain.
At Point B, the plankton levels are staying the same (steady) because the number of
mussels is staying steady, too. __________________________________________________________
2. Stopping to Think #2: (additional question) Define carrying capacity.
Carrying capacity is the amount (population) a container can hold (container meaning
area). BASED ON LIVING (biotic) AND NON-LIVING (abiotic) FACTORS
a. Look again at Graph 1. What is the carrying capacity of zebra mussels in Lake Ness? How did
you determine this?
The carrying capacity of zebra mussels in Lake Ness is approximately 2000. At that
point (in year 6) the ZEBRA MUSSELS population levels out.
b. List some of the factors that might affect this carrying capacity.
Answers may vary. A complete answer includes PLANKTON AVAILABILITY.
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Activity 85 – Answer Key
3. Stopping to think #3- Use the graph on page E-74 to answer the following questions.
a. What is the carrying capacity for zebra mussels in Lake Ness between years 13 and 25?
The carrying capacity of zebra mussels in Lake Ness between years 13 and 25 is
approximately 1000. (Population stays level, steady.)
b. Identify at least three non-living (abiotic) factors that may have caused the carrying capacity to
change. Explain how each factor could cause this change in carrying capacity.
Answers will vary. A complete answer will include QUALITY OF WATER (due to
presence of a factory built around the same time as year 10 on Graph 2)
c. Identify at least three living (biotic) factors that may have caused the carrying capacity to
change. Explain how each factor could cause this change in carrying capacity.
Answers will vary. A complete answer will include QUANTITY OF PLANKTON (due
to the relationship between amount of plankton and the number of zebra mussels. See
Graph 1.)
d. Do you think that the zebra mussel population will return to the level it had reached between
years 5 and 10? Why or why not? Answers will vary. A complete answer includes
the idea that if conditions return to what they were between years 5 and 10,
then the zebra mussel population should return also. ________________________
4. Stopping to Think #4- Is this a good experiment (on pg. E-75) to test the hypothesis that the factory is
affecting the zebra mussel population? Explain. _Answers will vary. A complete answer
includes that this experiment does not control for all the conditions (variables)
found between the two locations. Therefore it is not a good experiment.____________
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Activity 85 – Answer Key
Analysis:
1. Refer to the graph on page E-76 to answer the following questions:
a. What is the carrying capacity for owls in this habitat?
The carrying capacity for owls in this habitat is ABOUT 10—this is the point
at which the population become steady (levels out).
b. How did the carrying capacity change during this 40 year period? Explain.
The carrying capacity changed from approximately 20 to 10, therefore THE
LIVING AND NON-LIVING FACTORS CHANGED.
c. What living (biotic) and non-living (abiotic) factors might explain this change in carrying
capacity?
i. Biotic – availability of food (rodents, small reptiles); populations of
predators; competition with other species of birds
ii. Abiotic – change in weather patterns (climate); loss of habitat
(encroachment by development); natural disaster (volcano, flood,
hurricane)
d. Turn back to Activity 72, “The Miracle Fish” and look at Figure 2. Can you determine the
carrying capacity of Nile perch in Lake Victoria based on this graph? Explain.
No, carrying capacity cannot be determined because you don’t know how many other
fish are present. (180 metric tons caught includes all the fish species in the lake.)
2. Reflection: Consider the introduced species you have researched. Identify one ecosystem into which it
has been introduced. Do you think this species has reached its carrying capacity in this ecosystem?
Explain. _Answer will vary. We have only considered Nile perch and zebra mussels so far. We will
know more about introduced species after we finish the Invasive Species research project. ______
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