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The Wolf Effect. Adapted from Miller and Levine’s Biology 2010. Teacher Notes. The following is an activity adapted from Miller and Levine’s Biology 2010.
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The Wolf Effect Adapted from Miller and Levine’s Biology 2010
Teacher Notes • The following is an activity adapted from Miller and Levine’s Biology 2010. • In this activity, students will work in small groups (2-4 students) to research and answer questions based on a information given and available online. • This can be completed in a 40 minute time frame, or given out to be completed outside of class and discussed on a specified later date. • You will need power point access, online access, and printed information/question sheets for students if you desire to provide them.
Introduction • Read the following information about wolves in Yellowstone National Park and then, as a group, formulate answers to the following questions.
During the 1930s, hunting and trapping eliminated wolves from Yellowstone National Park. For decades, ecologists hypothesized that the loss of wolves--important predators of elk and other large grazing animals--had changed the park ecosystems. But because there were no before-and-after data, it was impossible to test that hypothesis directly.
Then, in the mid-1990s, wolves were reintroduced to Yellowstone. Researchers watched park ecosystems carefully and sure enough, the number of elk in parts of the park began to fall just as predicted. But, unpredictably, forest and stream communities have changed, too. Could a “wolf effect” be affecting organisms in the park’s woods and streams?
Opening Questions…. Explain why scientists predicted that reintroducing wolves to Yellowstone National Park would lead to a decline in the number of elk in the park?
Make a prediction….. Predict how fewer elk might affect other organisms in the park.
One of the favorite prey species of the wolves in Yellowstone is elk. • How do you think this relationship could affect the ability of certain plants to grow in Yellowstone? Remember, elk are herbivores…..
Yellowstone has high mountain slopes and valleys with streams. • Can you think of any reason why moose and elk might prefer to graze in one of those places rather than the other? • How do you think their preferences might affect Yellowstone’s plant communities? You have 2 minutes to discuss with your partner…..
What is one way in which life in Yellowstone’s streams might be affected by the presence or absence of plants along the stream banks? You have 2 minutes to discuss with your partner……
Eliminating wolves from Yellowstone National Park contributed to an increase in the number of elk. These elk grazed so heavily, especially along streams, that the seedlings and shoots of aspen and willows, and other trees, could not grow. Fewer trees led to fewer dams being built by beavers and to an increase in runoff and erosion. Aquatic food webs broke down, affecting birds, fish, and other animals.
The recent reintroduction of wolves has caused a decrease in the overall elk population and seems to have reduced elk grazing along certain streams. That may be in part because wolves are killing more elk and in part because elk have learned to stay away from places like stream banks and valleys, where wolves can attack them more easily.
In recent years, researchers have shown that streamside vegetation is exhibiting secondary succession and that aspen and willow trees are starting to grow back. There have been numerous other changes as well. Fewer elk mean more food for smaller animals. The increase in small prey, in turn, has brought diverse predators into the community. Carcasses abandoned by the wolves provide food for scavengers. In short, organisms from every trophic level have been affected by the Yellowstone wolves.
Let’s see what you’ve learned!!!! Complete the following for homework. Your responses must be neatly written or typed and handed in next class.
Make a Prediction… The Yellowstone wolf and elk are linked through a predator-prey relationship. If a disease were to strike the elk population, how would the wolves be affected?
Form an Opinion… Yellowstone is owned by the federal government. The reintroduction of wolves there angered nearby farmers because they feared their animals would be hunted. What level of responsibility do you think national parks should have toward their neighbors?
Making Connections…. Draw a food chain that connects Yellowstone’s wolves, aspen and willow trees, and elk. Then write a paragraph that explains why the Yellowstone wolves are a keystone species.
