Name: ____________________________
Ecology 1
Functional Response (Predator/Prey) Lab
Introduction:
Interactions between predators and their prey are important in 1) determining the populations of both
predators and prey, and 2) determining and maintaining the structure of a community. Many factors
enter into the ultimate outcome of predator-prey interactions. A predator must have the skills and
appropriate physical structure to be able to find, recognize, capture, and consume its prey. Prey try to
avoid predators by employing a variety of adaptations including physical, chemical, and behavioral
strategies. The habitat play an important role in determining the number of prey that can be supported,
whether the predator is present or not.
In this lab exercise we will simulate a simple predator-prey interaction involving arctic foxes and
lemmings. The scenario is that the arctic tundra is populated with lemmings searching for berries, grass,
and seeds so they can survive the coming winter. As the lemming population increases, due to
immigration and reproduction, arctic foxes and other carnivores in search of food are attracted to the
area.
In this activity, the field (habitat) is presented by a paper plate, the lemming population (prey) is
represented by beans, and the arctic fox population (predator) is represented by spoons. Following the
“rules of the community” set forth below, you will take many generations in this field, simulating the
effects of each on the population of the other over time.
Materials:
Paper plate (the field)
Beans (the lemmings)
Spoons (the arctic foxes)
Rules of the Community:
1. Initial lemming population: In each generation, there will always be at least 10 lemmings
initially present on the plate. The number of lemmings may be higher as determined by the
previous generation, but cannot be fewer than 10. For example, if you end a generation with 4
lemmings, doubling its population would bring you to 8. You must add 2 more so that you start
the next generation with 10.
2. Lemming survival and reproduction: At the end of each generation, the surviving lemmings will
double in number, as a result of reproduction and immigration, within a range of 10 and a
maximum of 100. If the number of surviving lemmings is at the end of a generation is so small
that doubling the population still results is less than 10 lemmings, you must bring the number
back up to at least 10 lemmings, as indicated in #1 above. If the number of surviving lemmings
at the end of a generation is so large that doubling the population will results in greater than
100 lemmings, you must add only enough lemmings to the population to reach the maximum of
100, as indicated in #3 below.
3. Lemming carrying capacity: The carrying capacity for lemmings in this field (plate) is 100
individuals. As indicated in #2 above, apply the doubling rule only if it does not cause the total
Name: ____________________________
Ecology 2
lemming population to exceed 100. If doubling the number of surviving lemmings would exceed
100, add just enough lemmings to bring the total population up to the 100 individual maximum.
Remember that this must be evaluated at the end of each generation.
4. Arctic fox minimum population: At the beginning of each generation there must always be at
least one arctic fox (spoon), presumed to have arrived there by immigration. If all of your arctic
foxes from a given generation survive, or move on, start each new generation with one arctic
fox that has immigrated to the area.
5. Arctic fox survival and reproduction: In order for an arctic fox to survive, or to decide to remain
in the field, it must capture at least 5 lemmings (in a single generation). Failure: If an arctic fox
captures 4 or fewer lemmings, it fails to survive, or decides to move on, and will not be present
at the beginning of the next generation. But remember, as indicated in #4 above, if you end a
generation with zero arctic foxes, a new arctic fox will migrate into the area so that you can start
the next generation with at least one arctic fox. Survival: If an arctic fox catches 5 or more
lemmings in a given generation, it will survive and will be present at the beginning of the next
generation. Reproduction: For every 5 lemmings that an individual arctic foxes catches in a
given generation, the arctic fox will reproduce and generate 1 offspring, which will then be
available at the beginning of the next generation to participate in the hunt. For example, in a
given generation, if an arctic fox captures 6 offspring, it will reproduce and generate one
offspring, making two arctic foxes available in the next generation. However, if the arctic fox
catches 11 lemmings, it will reproduce and generate 2 offspring, making three arctic foxes
available in the next generation.
6. Hunting: Arctic foxes will hunt for lemmings by running through the field. We will simulate the
hunt by slowly swiping a spoon across the plate one time per generation, attempting to scoop
up bean (lemmings) with no assistance from other spoons or hands. The number of beans
scooped up in the spoon represents the number of lemmings caught by the arctic fox for that
generation. For example, if a generation begins with a single arctic fox in the community, slowly
swipe the spoon across the plate one time and scoop up as many beans as possible, without any
other assistance. If there are 2 arctic foxes in the population, swipe spoons one at a time in
succession.
Procedure:
1. Head to the lab table with your group.
2. Follow the scenarios below for the first four generations, which are already recorded in Tables 1
and 2. Execute those written scenarios.
3. Generation 1: Begin with 10 lemmings on the field. Shake the plate to randomly distribute the
lemmings. Swipe the spoon (arctic fox) through the field and capture 1 lemming (data already
recorded). Arctic fox does not survive, or moves on, and will not enter the next generation. The
surviving lemming population doubles from 9 to 18.
Generation 2: Begin with 18 lemmings in the field. Shake the plate to randomly distribute the
lemmings. A new arctic fox migrates into the area, so you begin with only one arctic fox. The
arctic fox hunts and captures only 3 lemmings (data already recorded). The arctic fox does not
survive, or moves on, and will not enter the next generation. The surviving lemmings reproduce
and double their population from 15 to 30.
Name: ____________________________
Ecology 3
Generation 3: Begin with 30 lemmings in the field. Shake the plate to randomly distribute the
lemmings. A new arctic fox migrates into the area, so you begin with only one arctic fox. The
arctic fox hunts and captures 6 lemmings (data already recorded). This arctic fox survives and
can reproduce 1 offspring. The surviving 24 lemmings double to 48 lemmings.
Generation 4: Begin with 48 lemmings and 2 arctic foxes. Shake the plate randomly to
distribute the lemmings. Each arctic fox hunts. The first arctic foxes captures 6 lemmings,
survives, and reproduces 1 offspring (data already recorded). The second arctic fox captures 4
lemmings, does not survive, or moves elsewhere (data already recorded). The surviving 38
lemmings reproduce to 76 lemmings.
4. Generation 5: Begin with 76 lemmings and 2 arctic foxes. Shake the plate to randomly
distribute the lemmings. It is now time for you to hunt with your arctic foxes one after the
other. Count and record the number of lemmings captured by each arctic fox. Eliminate an
arctic fox if it catches 4 or fewer lemmings. Add an arctic fox for every 5 lemmings caught by the
parent arctic fox. New arctic foxes will hunt in the next round.
5. Generations 6-20: Repeat this process until you have results for 20 generations.
6. Data Table explanations:
a. Initial # lemmings is the number of lemmings you start with at the beginning of each
generation. It can be determined by doubling the # lemmings surviving at the end of
the current generation, unless the numbers are not between 10 and 100 (see rules of
the community).
b. Initial # arctic foxes is the number of arctic foxes that you should have at the start of
each generation. It can be determined for the next generation by adding # arctic fox
surviving with # arctic fox offspring at the end of the current generation.
c. # lemmings caught by each arctic fox (#1-#17) is the result of each arctic fox’s hunting
efforts in each generation. Space has been provided for up to 17 arctic foxes hunting in
the community at any given time. If you need more space, add additional rows at the
end of Table 1. You will not need all of the space provided for every generation (note
how the spaces for arctic foxes 2-17 have been shaded out for generations 1-3 and the
spaces for arctic foxes 3-17 have been shaded out for generation 4. NOTE: You do not
need to attempt to track the hunting efforts of a specific arctic foxes, just the total
number hunted by all of the arctic foxes.
d. # lemmings captured (∑) is the sum of all lemmings captured by all arctic foxes during
that generation. Add the numbers in the rows provided for # lemmings caught by each
arctic fox (#1-#17) for the given generation.
e. # lemmings surviving is the number of lemmings remaining at the end of a generation
after the arctic foxes has hunted and captured the lemmings. The surviving number of
lemmings can be calculated by subtracting the # lemmings captured (∑) from the initial
# lemmings.
f. # arctic fox surviving is the number of arctic foxes that survived because they
successfully captured 5 or more lemmings. To determine this, look at the # of lemmings
caught by each arctic fox (#1-#17) and count the number of cells which contain the
number 5 or greater.
g. # arctic fox offspring is the number of new arctic foxes added to the community as a
result of reproduction by existing arctic foxes. To determine this, look at the #
Name: ____________________________
Ecology 4
lemmings caught by each arctic fox (#1-#17) and add 1 offspring for every 5 lemmings
caught by each individual. For example, if 2 arctic foxes each caught 6 lemmings, you
would add a total of 2 offspring, one for each other those 2 original arctic foxes.
However, if you had 2 original arctic foxes and 1 caught 6 lemmings and the other
caught 13 lemmings, you would add 3 offspring, 1 for the arctic fox that caught 6
lemmings and 2 for the arctic fox that caught 13 lemmings.
Graph Presentation:
Prepare either by hand or by computer, three graphs as indicated below. Make sure that each graph
has 1) title, 2) labeled axes, 3) labeled axis units, and 4) labeled/differentiated lines.
1. Figure 1. Initial lemmings (m) and arctic fox (c) population size versus generation number.
The x-axis is the generation number, the y-axis is the number of individuals. This graph will have
2 lines (differentiate the lines by color, patterns, or symbols): one line for the initial number of
lemmings by generation and the other for the number of arctic foxes by generation.
2. Figure 2. Surviving number of lemmings (m) and arctic fox (c) versus the generation number.
The x-axis is the generation number, and the y-axis is the number of individuals. This graph will
have 2 lines (differentiate the lines by color, patterns, or symbols); one line for the number of
lemmings by generation, and the other for the number of surviving arctic foxes by generation.
3. Figure 3. Number of captured lemmings (m) and surviving arctic foxes (c) versus generation
number. The x-axis is the generation number, and the y-axis in the number of individuals. This
graph will have 2 lines (differentiate the lines by color, patterns, or symbols); one line for the
number of surviving lemmings captured, and the other for the number of surviving arctic foxes,
both by generation.
Results (Data): Attach Table 1 and Figures 1-3 to your Conclusion Questions.
Conclusions (Questions): For full credit, these questions should be answered thoroughly, in complete
sentences on a separate sheer of paper.
Part I:
1.
2.
3.
4.
Which population (lemmings or arctic fox) shows the first increase in numbers? Why?
Describe the change in the lemming population over the course of the 20 generations.
Describe the change in the arctic fox population over the course of the 20 generations.
Describe the relationship between changes in the lemming population relative to changes in the
arctic fox population.
5. Which of the three graphs you prepared best illustrated the relationship between changes in the
lemming population relative to changes in the arctic fox population? Why?
Part II: (Lemming Readings)
1. What other predators influence the population cycle of the lemmings?
2. How are scientists explaining the pattern exhibited by the lemming? (Provide details!)
3. Myth vs. Reality - What is really occurring with the lemmings compared to what the 1958 Disney
documentary “showed”?