Activity 84: Clam Catch (KEY)
Learning Target: We will OBSERVE how an introduced species affects a native species
population.
Before Activity:
1. Imagine an ecosystem in which most things stay the same from year to year. There is no change in the types of
species found there, and the average yearly rainfall, temperature and other conditions stay about the same.
Would you expect the population of each species to stay the same each year? Why or why not?
_If there is no change in the biotic or abiotic conditions, the population of each species would stay
the same, because there would not be any changes to the carrying capacity .______________________
2. Tomorrow you will be playing a game to model the size of a clam population over a ten-year period with the
same scenario as in #1. Do you expect the population of clams to stay exactly the same in each year of the
game? Do you expect a population of real clams to stay the same? Explain.
_Answers will vary. A complete answer includes that a model population stays stable (within the
carrying capacity). A real population should also stay stable over time (if the model is good.) _______
Define-Competition: _Two or more species seeking to gain access to a limited supply of a resource (like food)._
Part One: Clam Catch
1. Complete the game with your teacher and classmates.
2. Complete the following data table: (Period 1)
Year
Population of Clams
Year
Population of Clams
Initial
5
5
8
1
8
6
9
2
6
7
8
3
12
8
8
4
14
9
9
1
Activity 84: Clam Catch (KEY)
Year
Population of Clams
Year
Population of Clams
Initial
5
5
6
1
8
6
8
2
8
7
14
3
7
8
4
4
9
9
8
(Period 3)
Year
Population of Clams
Year
Population of Clams
Initial
5
5
12
1
5
6
3
2
4
7
3
3
8
8
6
4
12
9
10
3. Look at your data.
a. Was the population of clams the same from year to year? If not, what prevented the population of
clams from continuing to increase? __The clam population varies year to year. Availability of food
appears to limit further growth.________________________________________________________
b. Overall, was the population stable or unstable? Why? __The population became stable at between
7 and 8 clams. The high was 14 and the low was 5. ______________________________________
2
Activity 84: Clam Catch (KEY)
Part One Analysis:
1.
Graph the populations of clams over time from part one. Use a line graph, label your axes and title your graph.
SEE Activity 84 (KEY) SUPPLIMENT for GRAPH 1
2. Describe how this population of clams changed over time. _The clam population rose and fell, and
stabilized around 8.5 clams (carrying capacity).________________________________________________
Part Two: Competition
1. Complete part two with your teacher and classmates.
2. What happens if there are more organisms in an ecosystem than resources? Do you have any examples of one
species outcompeting another from your research on introduced species? __Answers may vary. Any
example of a competing non-native invasive species is acceptable. _____________________________
3. Complete the following data table: (Period 1)
Year
Population of
Population of
Clams
Zebra Mussels
Initial
8
2
1
7
2
Population of
Population of
Clams
Zebra Mussels
5
5
11
5
6
4
16
10
6
7
2
4
3
4
10
8
5
10
4
3
14
9
3
14
3
Year
Activity 84: Clam Catch (KEY)
Complete the following data table: (Period 2)
Year
Population of
Population of
Clams
Zebra Mussels
Initial
8
2
1
6
2
Year
Population of
Population of
Clams
Zebra Mussels
5
3
14
4
6
3
14
6
7
7
3
24
3
3
13
8
0
6
4
3
14
9
0
12
Population of
Population of
Clams
Zebra Mussels
Complete the following data table: (Period 3)
Year
Population of
Population of
Clams
Zebra Mussels
Initial
10
2
5
1
7
1
7
4
6
2
14
2
2
6
7
0
14
3
4
10
8
0
20
4
6
16
9
0
9
4
Year
Activity 84: Clam Catch (KEY)
Part Two Analysis:
1. Graph the population of clams and zebra mussels over time from Part Two. Use a line graph, label your axes and
title your graph. Use a key to show what represents the clam population and which represents the zebra mussel
population.
SEE Activity 84 (KEY) SUPPLIMENT for GRAPH 2
2. How did the population of clams change over time? __The population of clams fell (crashed) over time. __
3. How did the population of zebra mussels change over time? _Zebra mussel populations all increased.
4. What happened to the clam population after zebra mussels were introduced? _After the zebra mussels were
introduced, the clam population went down.___________________________________________________
a. Why did zebra mussels have this effect on the clam population? Explain. _The zebra mussels are
competing with the clams for a limited supply of food (plankton). ___________________
5.
In a real lake, what non-living factors might affect the size of clam and zebra mussel populations? List them.
__Answers will vary. At least TWO non-living (abiotic) factors must be included. Potential answers
include: AMOUNT OF SUNLIGHT, OXYGEN/CO2 LEVELS IN WATER, WATER LEVELS (RAINFALL OR
SURFACE FLOW), SOIL PARTICLES IN WATER, DISSOLVED MINERALS, CHEMICAL POLLUTION. ________
6. In a real lake, what living factors might affect the size of clam and zebra mussel populations? List them. __
Answers will vary. At least TWO living (biotic) factors must be included. Potential answers include:
OTHER COMPETITORS FOR PLANKTON, CLAM PREDATORS, MUSSEL PREDATORS, PHYTOPLANKTON
POPULATION CHANGES, ZOOPLANKTON POPULATION CHANGES, CHANGES IN ALGAE LEVELS. ______
5