Image courtesy of ODFW
True to their role as a keystones species in the Greater Yellowstone Ecosystem,
the return of wolves resulted in what ecologists call a trophic cascade - a top
down series of events that rippled through the ecosystem. Through predation,
wolves reduced the elk population which had been overgrazing the plant life. In
addition, with the presence of wolves, elk were no longer comfortable munching
plants in one area. As a result, there was a rejuvenation of plant life which resulted
in an increase of the many species dependent upon these plants. One such
species was the beaver. An increase in beaver dams created pond habitat for
many aquatic animals.
In addition, scavenger species benefited from the food provided by wolf kills.
Biodiversity returned to the Yellowstone ecosystem.
The more biodiverse an ecosystem is, the healthier it is. Changes to part of an
ecosystem can have positive or negative impacts on the entire ecosystem – ie.
the absence and presence of wolves.
Analogy: Consider the planet as one huge jigsaw puzzle. If a piece of the puzzle
is missing, is the puzzle complete? The interconnection of all pieces is essential.
The return of wolves in Yellowstone helped to put many pieces back in the ecosystem’s puzzle.
Students will be able to explain the meaning of biodiversity.
Students will be able to explain how the absence or presence of wolves within the ecosystem affected the ecosystem as a whole – from the impact on other species to the plant community and the health of the river itself.
Biodiversity: bio = life diversity = variety
The variety of living things within a habitat or ecosystem, including plants, animals and microorganisms
Keystone Species: A plant or animal that plays a disproportionately large role in the ecosystem – impacting both the prevalence and population levels of other species within their community.
Ecosystem: A biological community of interacting living and non-living organisms. There is a connection with between each species.
Each organism has its’ own niche or role to play.
Scavenger – An animal which eats animals that other predators killed
Trophic Cascade - This term refers to a top-down cascade where the top predator controls the population of primary consumers. The removal of predators which are at the top level of food chain can alter the food web dynamics.
Prerequisites for all activities:
1. Show one of the following videos:
“Wolves of Yellowstone” https://www.nationalgeographic.org/media/wolves-yellowstone/
“How Wolves Change Rivers” https://www.filmsforaction.org/watch/how-wolves-change-rivers/
2. Show the videos a second time – have students write down the “characters” (animals/ plants/river) in the video. Discuss: Pre-/post wolf population change for each character (more/ less – and why)
Supporting Handout: The Food Web
Activity 1 - Biodiversity Flowchart
Create a Flow Chart of the Yellowstone story of how wolves affected the ecosystem.
1. Play the wolf ecosystem video – pause to explain some of the things that were said. Students begin to create a flow-chart of the events
2. Play the video a second time - pause as needed for the students to add to or correct their information. Rewind the video on student’s request.
3. Divide class into smaller groups - students share their flowcharts with others in their group and add to their pictures/words when seeing others' flow-charted ideas.
4. Share some flowcharts with the class and discuss.
Follow-up activities -
– Express the flow-chart in a written form – one to three paragraphs
– Create a classroom mural, poster, or play to share with others - see Activities 3, 4 and 5.
Activity 2 – Biodiversity Game
1. Optional - Soccer ball with numbers 1-12 either written on the balls squares or, to avoid writing on the ball, write on masking
Ball alternative – pieces of paper numbered 1-12
2. Yellowstone biodiversity handout
3. Answer papers -
On three pieces of paper, students write the words Scavenger/ More plants/ Cool clean water - one word or phrase on each paper.
Papers can be color coded. These answer papers encourage participation from all students. Alternatively, write these three words/phrases on the board.
1. Review the basic sequence of events when the wolves returned- More Wolves/ Less Elk Eating Plants/ More Plants
2. Review: The return of wolves resulted in an increase in biodiversity due to indirect benefits to many other species including those in the handout. Discuss reasons why other species benefited indirectly from the presence of wolves.
Three main contributing factors include:
1) Scavengers - scavengers benefited from the carcasses of the animals which wolves killed
2) More plants - many species benefited from the increased growth in plants
3) Cool clean water - The increased growth in plants along the river shaded the river decreasing water
temperature and the plant's root system helped to stabilize the soil and river bank resulting in less erosion.
3. Project the Yellowstone Biodiversity handout on screen or give a copy of the handout to each student.
Discuss the title: Keystone Species increases Biodiversity. Define “biodiversity” and “keystone species”
4. The game:
To determine which picture in the handout will be chosen, a) If using a soccer ball, whoever catches the ball will find the number closest to their right thumb, 2) student picks one of the pieces of paper numbered 1-12 or 3) students simply choose of the of the pictures
5. Question: How did ______ (whichever picture was chosen) indirectly benefit by the return of wolves?
Students hold up one, two or three of the papers (scavenger/more plants/ cool clean water) which helps to explain the benefit.
For example: Eagle would have all three answers: Scavenger; More plants (for nesting/ perching) and Cool clean water ( for the fish they eat). Many specie benefited for a combination of reasons. Encourage students to explain their answer, connecting it with the return of wolves.
Some answers can be more complex. For example, the frog benefited from the ponds that beavers created thanks to the increase in trees due to less elk browsing due to being hunted by wolves or an increased fear of wolves. (In Yellowstone, beaver colonies increased from one to nineteen in 20 years after the return of wolves.)
Activity 3– Biodiversity Mural - Click here for examples
Objective: Students will work together to create a mural that will give an effective visual of Yellowstone NP, without and with wolves.
This activity has been used by several teachers, each with its unique method and flair!
This activity follows the prerequisites of the video and discussion of the sequence of events (above) – what led to what and why.
The mural give students a great opportunity for them to practice the art of teamwork -using wolves as their role model!
Large sheet of paper, the size to fit the wall/ space where it will be displayed
Materials that can be used to create the animals/ plants – crayons/ paints/ markers/construction paper for creating cut-out figures
1. In preparation for creating the mural, students may watch the video several time with the goal of identifying all the players and each step of the chain of events. List these on the board. Students should copy on their papers.
2. Together, students decide the method they want to use to construct the mural.
3. Discuss A) Yellowstone NP without wolves – what might it have looked like? What species might one see – which species had large populations/ which had less/ which species were absent?
B) Yellowstone with wolves – what does that look like? Same process as above.
4. Groups of students may take on sections or species as their contribution. How this works will depend on the format of the mural. Students should be encouraged to take the lead as much as possible. Decide on any words of explanation that they want to include.
If the mural can be hung in the school hallway, it can then serve as a way to educate other students in the school about the importance of wolves and the amazing role they play in the ecosystem.
Biodiversity images - These drawings by Maren Salomon can be used in creating the mural.
Activity 4 – Biodiversity Poster
This activity is a scaled down version of the mural. It can be created individually or in paired/ small groups.
Leading scenario to help students decide on the focus of their poster: You are working in Yellowstone. While most tourists know that wolves live here, they don't understand the "big deal" - why wolves are important. What difference does it make whether there are wolves or not? Create a poster that will educate as well as help to change the tourist's opinion on the importance of wolves.
Follow steps 1 - 3 of the above mural activity. Students may depict Yellowstone before and after wolves or only after the reintroduction of wolves. Alternatively, two students or groups may choose to pair up - one making a "before" and another making an "after" poster
Activity 5 - Biodiversity Play
One of the ultimate goals for a unit on wolves is to take some action to help the wolves. Perhaps the best way young people can help is to share what they have learned with others - their friends and family. In addition to murals and posters, turning the story into a play gives the students a very fun way to teach other classrooms about the importance of wolves. This could also be given during a parent night at school.
Because of the large cast of characters in this story, the entire class can be involved. Each student will take on the role of one of the plants or animals. Students can make their own costumes. One or more students could be the narrator. Students will act out the story of Yellowstone. If the audience is grade 3 and above, they may choose to begin with biodiverse Yellowstone - then the story of all the wolves being hunted and the impact on the other animals - then the return of wolves and resulting biodiversity. Audience participation could be encouraged in predicting the decrease/ increase of species. This activity is limited only by the student's creativity. Talking animals are allowed! Perhaps a musical?
This is a multi-curricular activity - science, language arts, art.