Subject: Loop of the Week

Posted by Linda Booth Sweeney on 11/1/2003
In Reply To:Loop of the Week Posted by John Sterman on 11/1/2003

Message:

John,
Thanks so much for sending this along and for your provocative
commentary. I have found similar examples. And they haunt me!

Our boys have a poster in their bedroom on food chains (produced by
Frank Schaffer).The picture shows an open loop that connects plants
to smaller animals (worms and mice) to larger animals (such as
hawks). Instead of closing the loop and showing the connection back
to decomposers, the text and visual suggests a one-way, open-loop of
causality from green plants to animals at the top of the food chain.
The text on the poster reads:

"A food chain shows how things depend on one another for food. Green
plants get energy from the food they produce. Some animals get
energy by eating plants. Other animals get energy by eating animals
that have eaten plants."

In my own review of middle-school and high school text books (and in
a review conducted by Barman (1994)) I found that energy transfer in
ecosystems is most often represented in terms of linear chains and
food pyramids and infrequently represented as webs and causal loops.
In my dissertation ("Thinking about Systems") I show how students'
(and their teachers) describe "cycles" (typically used to mean
repeated sequence of events), "food chains" and "chain reactions" in
situations in which feedback structures exist.

None of this is surprising... it just adds fuel my fire... our every
day artifacts (including our children's text books, posters, our
newspapers, even museum displays) need to do a much better of job of
fostering people's potential to think about systems (particularly
closed loops and stock/flow structures)

Linda