Animal Barometers of the Food Chain (PCEC)
Predators at the top of the food chain act as environmental barometers. Pesticides that accumulate in the environment affect both predators and their prey.
4 and up
Indoor or outdoor classroom
Potlatch Conservation Education Center at Cook’s Lake, Casscoe
Education Program Coordinator, 870-241-3373
30 minutes - 1 hour
Suggested Number of Participants:
20 - 25
One adult supervisor per 10 students; outdoor activities, weather permitting.
- Explain the relationships between predators and prey.
- Describe how predators are an ecological barometer.
*See glossary for definations
- Approximately 30 “food chips” per participant (white and colored poker chips with 2/3 white to 1/3 colored)
- One name tag per participant
- One small paper bag per “aquatic insect”
When something disrupts the food chain at the bottom, it is magnified at each succeeding level. When it reaches the top, the disturbance is a major environmental disruption. Raptors and other predators at the top of the food chain are especially vulnerable when the chain is unbalanced; thus, they are good environmental barometers. Because of this environmental barometer, people now realize the potential danger to humans and are finding safer pesticides.
- Divide the participants into three groups. In a class of 26, for example, there should be two “bald eagles,” six “fish,” and 18 “aquatic insects.” (There should be three times as many fish as bald eagles and three times as many aquatic insects as fish.) Give each participant a nametag that identifies what species he/she is.
- Give each “aquatic insect” a small paper bag, which represents his or her stomach. Distribute the “food chips” around a large open space.
- The aquatic insects look for food first. The bald eagles and fish are to watch quietly on the sidelines. (The predators are watching their prey!) The insects have 30 seconds to collect as much food as possible and put it in their stomachs (bags).
- The fish are now allowed to hunt the insects while the bald eagles remain on the sidelines. The amount of time allowed depends on the size of the playing area. Sixty seconds could be given in a large playing field. Each fish should have enough time to catch one or more insects. Each insect caught by a fish (tagged) must give its bag of food to the fish and sit on the sidelines.
- Next the bald eagles hunt the fish with fifteen to 60 seconds of hunting time. All fish that are caught must go to the sidelines. Any fish still alive may continue to hunt for aquatic insects, and the remaining insects can continue gathering food chips. The bald eagles simultaneously hunt the fish. At the end, all participants should gather in a circle with their food bags.
- Ask all participants who are “dead” to identify what predator ate them. Next, ask the bald eagles to empty their food bags and count the white pieces and colored pieces in their “stomach.” Write down the results. Then have any “living” insects and fish count their food and list these results also.
- Tell the participants that each colored food chip represents DDT, a pesticide that was sprayed onto nearby forests to combat insect damage and loss of timber. This pesticide is highly toxic and often is carried into the surrounding water systems where it accumulates in the food chain. Therefore, all aquatic insects not eaten by fish may now be considered dead from the pesticide if they have any colored food chips in their stomach. Any fish with half or more of their food supply contaminated are also dead. The bald eagle with the highest number of colored food chips will not die yet. However, it has accumulated so much pesticide in its body that the eggshells it produces next nesting season will be so weak that the eggs will break. The other bald eagles are not visibly affected at this time but will continue to accumulate pesticides to toxic levels as long as they eat contaminated prey.
- What are their observations about the food chain, how it works, how toxic substances can enter the food chain and how it affects both predators and prey at all levels of the pyramid?
(Adapted from The Raptor Center’s “Predator/Prey Relationships” by Carolyn Lane on the Internet site www.raptor.cvm.umn.edu/raptor/meeen/no3.html.)
Participants research other toxic substances that might find their way into a food chain. How could other substances affect humans? How could this be prevented?
- What happens in a food chain when toxic substances enter it?
- What, besides DDT, could be considered a toxic substance? Source?
- Could this toxic magnification affect humans? How?
Biomagnification – bioaccumulation of a substance in smaller organisms that are food for larger organisms in the food chain; sequence of processes that result in higher concentrations in organisms at higher levels in the food chain
Food chain – feeding order in an ecological community that passes food energy from one organism to another as each consumes a lower member and in turn is preyed upon by a higher member
Pesticide – synthetic and sometimes biological substance used to kill or contain pests