Limiting Factors Graphing Activity Key
Some limiting factors are density independent
(Factors that limit the growth and size
of populations but are not due to the
size of the populations)
 Weather/seasonal cycles/sun spots
 Natural disasters
 Fires
 Human activities like damming rivers and
clear cutting forests
Some limiting factors are density dependent
(Factors that can limit the growth and size of a
population due to the size of populations)
 Food
 Available space/habitat/nesting sites
 Competition
 Predation
 Parasitism
 Disease
Directions: Use the data in the tables on the right side to plot the three sets of data on one graph.
50,000
Woody Browse
25,000
1,000
500
250
Snowshoe Hare
100
50
25
10
5
1
Predators/Lynx
0.50
0.25
-1 0 1 2 3 4 5 6 7 8 9 10 11 12
Note: (Graph and data Adapted from Keith 1974)
Woody browse (winter food for hares)
Plot these points with a green colored pencil, and
then draw a line connecting the points.
Years
Relative Biomass
-1
28,000
1
50,000
5
50,000
6
25,000
9
25,000
11
50,000
12
50,000
Snowshoe hare
Plot these points with a blue colored pencil, and
then draw a line connecting the points.
Years
Relative Biomass
-1
30
0
30
5
1,000
9
30
10
30
12
125
Predators (such as the Lynx)
Plot these points with a red colored pencil, and
then draw a line connecting the points.
Years
Relative Biomass
-1
0.30
1
0.30
5
1
6
1
9
0.30
11
0.30
12
0.45
Once you have plotted the points from the
table, it is time to analyze the results.
Limiting Factors Graphical Analysis of the Vegetation-Herbivore-Predator Cycle
Name: _______________________________________Period:_____________Date:_________________
First consider some background information:
On the y-axis, biomass is given in kilograms per hectare. Biomass is the mass of living matter. Living
things have mass. As living organisms are able to get the resources they need, they survive and
produce offspring. The population grows in size and contributes more biomass to a given area. The
data you have been given is the biomass for three types of organisms measured over time. The x-axis is
the independent variable, time. You will use this graph to examine density dependent and density
independent limiting factors.
Complete the following:
1. Write "Predators/Lynx” above the red line, “Snowshoe hare” above the blue line, and “Woody browse”
above the green line (winter food for hares, consisting of leaves, twigs, and the buds of woody plants).
2. Examine the green line for the woody browse (the food for hares) from the first to the fifth year. Did
the biomass of the food available increase, decrease, or stay the same (constant) over these years?
The biomass stayed constant
3. Examine the blue line for the biomass of the hare populations from the first to the fifth year. Did the
biomass of the hares increase, decrease or stay constant? It increased
4. What resource contributed to the biomass increase seen in the hare populations? Food availablility
5. Examine the red line for the biomass of the predators/lynx from the first to the fifth year. Did the
biomass of the lynx increase, decrease or stay constant? It increased
6. Why did the biomass of the predators change over the first five years? Food supply constant (hares/prey)
7. Examine the green line (food for hares) between year 5 and 6. Did the biomass of the food supply for
the hares increase or decrease? It decreased
8. What do you think a decrease of the food supply for the hare populations will do to the biomass of
the hare population? Examine the blue line for the biomass of the hare populations between years 5-9
to help you answer this question. Decreased food supply will cause hare populations to decrease
9. If the predators, the lynx, eat the hare as prey, what will happen to the biomass of the predators if the
biomass of their food source declines? Examine the red line between years 5 and 6, and you will see
that at first the predator/lynx biomass stayed constant, but then examine the red line between years 6
to 9. Explain what happened to the biomass of the predators, and explain why you see this change.
The lynx biomass decreased in response to the decreased food (hare/prey) supply.
10. The blue line shows a decrease in the biomass of the hares from years 5 to 9, and this meant the
populations of the hare decreased significantly because their food source (green line), the woody
browse, decreased from years 5 to 6. Now, look at the green line between years 6 to 9. Did the biomass
of the woody browse (food for the hares) continue to decrease, or did it stop decreasing and level off to
a constant amount? It became constant
11. Look at the green line, the biomass for the woody browse (food for hares), between years 9 to 11,
and you will see that the woody browse was able to recover and increase in biomass. Why?
Because the hare population decreased, so they ate less woody browse, and so the woody browse
could recover
12. As the biomass for the food source for the hares started to increase, what effect did this have on the
biomass of the hares between years 9 to 10? Look at the blue line between years 9 and 10. Did the hare
populations continue to decrease, or did they level off and become constant? It became constant
13. When the hare biomass became constant between years 9 to 10, what happened to the biomass of
their predators, the lynx, between the years 9 to 11? Did the biomass of the predators (red line) stop
decreasing, and if so, why? The decrease stopped and became constant because the food supply was
constant.
Once the biomass of the woody browse increased during years 9 to 11, it increased the food supply
for the hares, and the hare biomass stopped decreasing and leveled off. The biomass of the hares then
began to increase between years 10 to 12 because the environment could feed more hares. When the
biomass of the hares increased, this made more food available to their predators, the lynx, and their
biomass increased between years 11 and 12. This is a predator-prey cycle that is related to a
vegetation-hare interaction.
14. Look at the green line between the years of 11 to 12 again. What do you think will eventually happen
to the biomass of the food supply of the hares? Do you think it will stay constant, or do you think it will
increase or decrease? Support your answer. It will stay constant until there are too many hares for
this resource. As hare populations increase, the food supply will probably start to decrease again.
15. List two or more density dependent and density independent limiting factors that you think impact the
biomass of the following organisms:
Woody Browse
Hare
Predators/Lynx
Density Independent
Weather
Fires
Clear cutting
Seasonal cycles
Natural disasters
Human activities
Fires
Weather
Human activities
Space/light
Nutrient Availability
Disease
Food
Competition
Predation/disease
Food
Space
Parasitism
Density Dependent