Predator / Prey Relationships
7th Grade Environmental Science
Mrs. Krempa
Name ____________________________________
Date & Section ____________________________
What goes up must come down! Predators and their prey do not simply interact with one another on an
individual basis. They also affect one another on the level of populations. In fact, the size of the prey
population has a strong affect on the size of the predator population and vice-versa. The following graph
shows how the size of the Lynx and Snowshoe Hare populations in Canada changed over time. The data is
based on the number of animal skins bought from trappers. Examine the graph and answer the questions.
1. What happens to the Lynx population when the Snowshoe Hare population goes up?
____The increase in the Hare population would cause the Lynx population to go up too because there
____ is more food for the Lynx (Lynx eat Hares). ____________________________________________
2. How would you expect the increasing Lynx population to affect the Snowshoe Hare population?
Explain.
_____ The increase in Lynx population would cause a decrease in the Hare population because there
_____ are more Lynx eating more Hares. _________________________________________________
3. What happens to the Lynx population when the Snowshoe Hare population goes down? Why do you
think this happens?
______The decreasing Hare population would cause a decrease in the Lynx population. ___________
_______Less Hares means less food for the lynx to eat so some of the Lynx will die or move out._____
4. How can you tell that Lynxes feed almost exclusively on Snowshoe Hares?
Look at the graph… The Lynx line directly, immediately and perfectly follows (shadows) the Hare
line. The Lynx line is a mirror copy of the Hare line! If the Lynx ate something else – added to
their food source – when the Hare population dropped, the Lynx would eat their other food source
instead of the Hare. The Lynx population would still go down with the Hare, but the Lynx would
not drop as low as the Hare because the Lynx is eating something else along with the Hare.
5. What factors other than its interaction with the Lynx might affect the population of Snowshoe Hares?
_____Factors that affect population growth – disease, habitat destruction, food supply, natural disasters,
_____ competition (other predators), climate/weather… ________________________________________
6. Suppose that fur coats made of Lynx became very popular. How would this initially affect the Lynx
population? The hare population? What would this make the graph look like?
_______The demand for more Lynx fur would GREATLY decrease the Lynx population. The Hare
_______ population would rise very quickly without any Lynx to eat them. The graph would show the
_______Lynx line crashing almost straight down and the Hare line rising almost straight up. __________
7. What long term effects might this (#6) have on the population of Snowshoe Hares?
________Immediate effect – Hare would overpopulate. Long term effect – Hare population would crash
_______ and burn due to overpopulation. (could be disease, lack of resources…) ___________________
8. How would the change in population of Snowshoe Hare in #6 possibly affect the Canadian ecosystem?
The Hare population was WAY over carrying capacity in #6….
Possible effects – eat all plants (strip ecosystem of resources), no food for other species,
crowd out other species (take all of the available niches), decrease diversity (only bunnies left!)