Limiting Factors Graphing Activity

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

25,000

1,000

500

250

100

50

25

10

5

1

0.50

0.25

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

-1 0 1 2 3 4 5 6 7 8 9 10 11 12

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. Didthe biomass of the food available increase, decrease, or stay the same (constant) over these years?_____________________________________________________________________________________

3. Examine the blue line for the biomass of the hare populations from the first to the fifth year. Did thebiomass of the hares increase, decrease or stay constant? _____________________________________

4. What resource contributed to the biomass increase seen in the hare populations? _______________

5. Examine the red line for the biomass of the predators/lynx from the first to the fifth year. Did thebiomass of the lynx increase, decrease or stay constant? ______________________________________

6. Why did the biomass of the predators change over the first five years? _________________________

7. Examine the green line (food for hares) between year 5 and 6. Did the biomass of the food supply forthe hares increase or decrease? _____________________

8. What do you think a decrease of the food supply for the hare populations will do to the biomass ofthe hare population? Examine the blue line for the biomass of the hare populations between years 5-9 to help you answer this question. _________________________________________________________

9. If the predators, the lynx, eat the hare as prey, what will happen to the biomass of the predators if thebiomass 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. ____________________________________________________________________________________

10. The blue line shows a decrease in the biomass of the hares from years 5 to 9, and this meant thepopulations of the hare decreased significantly because their food source (green line), the woodybrowse, decreased from years 5 to 6. Now, look at the green line between years 6 to 9. Did the biomassof the woody browse (food for the hares) continue to decrease, or did it stop decreasing and level off to a constant amount? ___________________________________________________________________

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?

____________________________________________________________________________________

____________________________________________________________________________________

Once you have plotted the points from the

table, it is time to analyze the results.

12. As the biomass for the food source for the hares started to increase, what effect did this have on thebiomass 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?_____________________

13. When the hare biomass became constant between years 9 to 10, what happened to the biomass oftheir predators, the lynx, between the years 9 to 11? Did the biomass of the predators (red line) stopdecreasing, and if so, why? ______________________________________________________________

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 theirbiomass increased between years 11 and 12. This is a predator-prey cycle that is related to avegetation-hare interaction.

14. Look at the green line between the years of 11 to 12 again. What do you think will eventually happento 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. ________________________________________________

__________________________________________________________________________________________________________________________________________________________________________

15. List two or more density dependent and density independent limiting factors that you think impact thebiomass of the following organisms:

Woody Browse Hare Predators/Lynx

Density Independent

___________________

___________________

___________________

___________________

___________________

___________________

___________________

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Density Dependent

___________________

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