A Little Bit More
Most of us are aware that in any healthy natural system there is a tangled web of organisms that rely on each other. Any changes to that web can affect other areas in ways that can’t be predicted and yet humans continue to manipulate the natural environment to suit their own needs/wants. Most of us also know about food pyramids with different levels of organisms depending on those on the lower levels. Although predators are at or near the top of these pyramids, the “story” that unfolded in Yellowstone, showed that environmental effects can be from the top of the pyramid down as well as from the bottom up.
When the wolves (many other predators were eliminated too) vanished from Yellowstone in the early 20th century, there were many well-meaning reasons for doing so but little understanding of what effect this might have on the overall biodiversity (variety of organisms) of the Park. Not until wolves were reintroduced in the 1990’s and their population expansion and effects in the northern portions of the Park were documented did it become clear how important the wolves actually were.
Basically, this is what happened when the wolves were removed from Yellowstone Park. The wolves were no longer preying on Elk so the Elk population grew and the animals were able to congregate in rather large herds to feed placidly and heavily on aspen and willows along the waterways. Within a short period of time, the aspen/willow population was dramatically reduced and Beavers, which relied on these trees as food and building materials, left the Park. With the Beaver population gone, the valleys where Beaver ponds used to exist, dried up and no longer fed the streams with cold, water for the trout. Furthermore, areas around the ponds that had been moist and had abundant trees in the past could no longer support many trees so songbird populations also were dramatically reduced. This didn’t happen overnight but as this domino effect unfolded, scientists were puzzled as to exactly what was causing the changes. Not until the wolf was reintroduced in 1995-96 and researchers saw a change in Elk feeding patterns, then a return of trees, then Beaver, then trout and songbirds, were they able to put all the pieces of the puzzle together. The wolves are an integral part of the system that kept the Park environment healthy and whole.
Activities
Science – Local Food Web
Objectives: Create a food web that’s applicable to your own area
Materials: Materials: 3X5 cards, bulletin board, string, access to the web
This unit’s focus is really on a mini food web that was interrupted when the wolves of the Yellowstone Park were eliminated. The removal of a single organism may or may not disrupt a food web as dramatically as in Yellowstone but it’s always important to be aware of that possibility.
This may be an activity you’ve already done but if you haven’t or if you haven’t tried doing it with local animals and plants, I think it has value to do again.
- Take a look at the web sites provided to see what a food web looks like. Make sure your students understand what is meant by a “food web” rather than “food chain”.
- Now ask your students to help you create a list of local organisms (at least 10 or one for every student in your class) that live in the same habitat – forest, field, lake or stream, desert, or wetland. Be sure you include at least one mammal, bird, reptile or amphibian, fish, insect, and spider along with at least one or two low-growing plants in your list.
- Once you have a list of local organisms, write the name of each organism on a 3X5 card and assign each student to at least one card. They’ll need to do a bit of research so they can write on the back of their card where their organism lives in your area within the habitat you chose, what it eats, and what eats it.
- Once the organism cards are filled out, have one student place their card on a bulletin board. Have the next student place their card on the board and if the first or second organism feeds on the other organism, attach a string between the two. Now have a third student place their card on the board and have them attach a string to any other cards that their organism feeds upon or that feeds upon it. If you have a reasonably large number of cards on the board after this process, you should have lots of string going from one card to the next in your food web.
- Be sure to point out that this is a very incomplete list and that there are many, many more organisms that could be placed up on the board. The web for your area is a very complicated web indeed but this little one should get them started thinking a bit more about their own local animals and plants and the relationships among them – it’s all interconnected.
Facts about Food Chains and Food Webs
Key Concepts
Food Webs /Food Pyramids, Environmental Issues, Predator/Prey Relationships, Populations and Ecosystems
Questions
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