Investigation 8
How Does Biomagnification
Affect Communities?
Introduction
In 1962, Rachel Carson wrote the book Silent Spring detailing the detrimental effects of the pesticide
dichlorodiphenyltrichloroethane (DDT). This literary work was hailed as the beginning of the environmental
movement and is credited with partial responsiblity for legislation banning the use of DDT. DDT was identified
as the cause of decline in populations of the charismatic megafauna species such as the Peregrine Falcon,
California Condor, and Osprey due to the thinning of egg shells when exposed to DDT.
Objectives
1. To determine how Biomagnification affects communities.
2. To determine relationships and build a representative food chain.
Materials
Pipe Cleaners
Plastic Bags
Procedure
1. Students will be divided into three separate groups: Owls, Shrews, and Grasshoppers. Student groupings
will be decided along the principles of Ecological Pyramids- there will be more producers than first order
consumers, more first order consumers than second order consumers, and more second order consumers than
third order consumers. Record the number of organisms at each trophic level below:
2. At the start of the activity, the students who are designated as “grasshoppers” will feed on “grass” (pipe
cleaners). The student grasshoppers will eat as much grass as is available to them. Record the grand average
number of green and red pipe cleaners per individual below:
3. Now, the students designated as “shrews” will feed on the “grasshoppers”. When the shrews feed on the
grasshoppers, the stomach contents of the grasshoppers (all of the pipe cleaners) are passed onto the shrew.
Record the grand average number of green and red pipe cleaners per individual below:
4. Finally, the students designated as “owls” will feed on the “shrews”. As before, when an owl “eats” a shrew,
the stomach contents of the shrew are passed to the owl. Record the grand average number of green and red
pipe cleaners per individual below:
5. How did the grand average (raw number) of the types of grass per organism change, as we ascended the food
change?
Study Questions
1. What is Biomagnification?
2. How does Biomagnification affect lower trophic levels vs. affecting higher trophic levels?
3. If DDT is only lethal at certain levels, who is most commonly affected?
4. In Northern Arizona, most fish and aquatic ecosystems have trouble with biomagnifications and mercury.
How would this affect humans?
5. How could biomagnification affect populations over time?
6. DDT is an insecticide that has broad use in killing mosquitoes. Is it more important to reduce outbreaks of
malaria in human populations, or to preserve biodiversity?
7. Do your own research: draw a food chain below, and indicate a substance that impacts the food chain.