Snowshoe hare and lynx populations
AIM: To investigate how predator-prey populations change through negative feedback
BACKGROUND:
Populations are always changing. Sometimes changes are the result of humans interfering with food webs or habitats.
But even when humans do not interfere, populations will still naturally shift up and down or fluctuate. For example,
let us study the relationship between the Canada lynx and its primary prey, the snowshoe hare.
To understand how the population of lynx and hares changes year to year, we need to collect information about the
number of individuals in a population. Unfortunately, it is impossible to count the exact number of hares in Canada in
any given year. Therefore, this information must be gained by capturing a small number of individuals and then
estimating the actual number out in the wild. For over 300 years, the Hudson Bay Company has been involved in the
fur trade in Canada. Detailed company records list the number of snowshoe hare pelts and the number of lynx pelts
collected by hunters and trappers every year since the late 1700’s.
In this investigation, your group will be simulating the changes in the two populations over time. The experiment will
simulate 25 generations of each species and the changes in number of organisms will be recorded. The data will then
be graphed to show a visual representation of how the two populations regulate each other.
MATERIALS:
flat surface of 60cm x 60cm
300 cardboard squares representing snowshoe hares
Graph paper
masking tape
1 cardboard square representing a lynx
population data table
METHOD:
1. Use tape to mark off a square, 60cm x 60 cm, on a table top or other flat surface. The square represents the
area inhabited by a population of snowshoe hares.
2. Begin the simulation by populating the habitat with three hares—spatially dispersed within the square.
3. Toss the cardboard lynx into the square in an effort to capture (i.e., land on any portion of) as many hares as
possible.
-In order to survive and reproduce, the lynx must capture at least three hares when tossed.
-With the hare population at this stage, lynx survival is virtually impossible.
4. Remove any hares captured and enter the tallies for the first generation.
5. The hare population doubles between generations—multiply “Hares Remaining” by two and enter the
resulting number in the “Number of Hares” column for the second generation.
6. Place the required number of hares in the square. If no lynx survived the previous generation just imagine
that another moves into the area.
7. Toss the newly recruited lynx—repeating step 2.
8. Remove any captured hares and enter the new tallies.
9. By generation 5 the lynx should be able to capture three hares when tossed. If successful, the lynx survives
until the next generation and also produces offspring—(one per each three hares captured.)
10. Toss the lynx square once for each lynx.
11. As the population builds it is important to separately tally each lynx’s kills, removing captured hares after
each lynx is tossed.
12. Determine lynx survival and reproduction using individual lynx capture numbers.
13. Remember, lynx produce one offspring for each three hares captured.
e.g. If a lynx captures seven hares, three lynx enter the next generation—the original lynx and two
offspring.
14. Individual lynx capture numbers should be tallied on a separate sheet of paper and only totals entered in the
table.
15. Between generations 9 and 11, the populations will probably crash back to, or near, zero. If and when this
happens be sure to begin subsequent generations with at least three hares.
16. Carry the simulation through 25 generations.
RESULTS:
Generation of
hares
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
No. of
hares
No. of lynx
3
1
No. of
hares
eaten in
total
No. of hares
remaining
No. of lynx
starved
No. of lynx
surviving
No. of lynx
offspring
produced
DATA PRESENTATION:
On the graph paper below plot a graph showing:
-generations on the x axis
-no. of organisms on the y axis
-plot the data from the second and third column in the table above
-you will need to draw 2 lines – use different colours to identify the lynx from the hare
ANALYSIS:
What patterns do you notice? Describe at least 3 patterns.
1.
2.
3.
First, let’s think about the hares.
As the number of hares decreases, what do you think happens to the population of grass and seeds that the hares
eat? Why?
After a few years, the hare population begins to increase. Why? On your graph, label these periods of prosperity with
arrows and a short description of what is happening in your own words.
Now, let’s think about the lynx which eats the snowshoe hares.
In general, are there more lynx or more hares? Why?
Do the peaks in the lynx graph line up exactly with the peaks in the hares’ graph?
When the hare population increases, what happens to the lynx population? Why?