How Do Predator and Prey Populations Interact?
An interaction between a species (predator) that feeds on another species (prey) is called a predator–prey relationship. For example, when snowshoe hares are abundant in a given area, the lynx population in the area is well fed and the survival rate of their offspring high. As a result, the lynx population grows as well. As the number of lynx increases, a larger number of snowshoe hares are eaten—resulting in a hare population decrease. As the population of hares decreases, the lynx population begins to decline as well.
The predator–prey relationship is an example of a density-dependent limiting factor. A density-dependent limiting factor affects the population density (number of organisms per a given area) when it reaches a certain level. Other examples of density-dependent limiting factors are competition, parasitism, and disease. As a population grows beyond the maximum population size that a particular environment will support (known as the carrying capacity), limiting factors act to reduce the population. The size of the population shrinks, then grows again, and so on. The resulting cycle of population changes may be repeated indefinitely.
In this activity, you will explore inter-dependencies in ecosystems by examining several predator-prey relationships.
Watch Video 1
Observe Part 1
Based on the data shown in Video 1 (provided below) what do you think would happen to the hare population if the lynx population became extinct? What would happen to the lynx population if the hare population became extinct?
Watch Video 2
Observe Part 2
How is the situation that Video 2 describes more complex than the dynamic described in Video 1?
Identify an Experimental Design Flaw
Describe two challenges you think might be associated with studies of predator-prey relationships in complex ecosystems.
Refine/Expand the Experiment
Describe at least three other factors that may influence the lynx and hare populations.
Practice Scientific Reasoning
Consider a home that has an increasing mouse population. In an effort to decrease the mouse population the homeowner brings a cat into the house and also places mouse poison throughout the house. In this scenario, is the homeowner able to determine which is more effective at reducing the mouse population, the poison or the cat? Explain.
Connect to Your World
Yellowstone National Park is a complex ecosystem with many inter-dependencies. For example, there is a complex dynamic between beavers, wolves, and elk that has been studied for many years. Prior to 1995, there was only one beaver colony in the park. After the reintroduction of grey wolves into the park the number of beaver colonies increased to nine. Why do you think the reintroduction of wolves into Yellowstone influenced the Elk population? How does the Elk population, in turn, exerted an indirect impact on the Beaver population?
Learn More by Exploring These Links
The following is a link to a card game that you can use to simulate the lynx-hare relationship:
If you would like to combine this activity with an in-school experience, try the following laboratory kit: