Subject: Feedback Loops

Posted by Linda Booth Sweeney on 2/8/2006
In Reply To:Feedback Loops Posted by Jay W. Forrester on 2/7/2006

Message:

Thank you for your posting Jay. It is helping me to clarify my own thinking about what is feedback and what isn't. Here is another potential, non-feedback example, similar to Phil's lighting example:

We have in my sons' room, a school poster depicting a typical food chain.
The poster depicts a sequence of relationships that connect plants to smaller animals (such as mice) to larger animals (such as raptors). Here is the text from the poster:

"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 (Schaffer, 1993)."

Jay has posited that "Everything that changes through time is controlled by feedback loops." This does not seem to hold true in the case of food chains or webs. There is an energy exchange occurring that is one-way and domino-like, and not comprised of feedback. Energy comes from the sun and eventually dissipates as one animal eats another. The energy itself doesnąt recycle, what does recycle is matter.

A more systemic view of a food web would be one in which decomposers are shown as part of the return loop for nutrients.

Like Phil, I wonder, am I missing something?

Linda Booth Sweeney

Follow Ups:

Feedback Loops - Prof. Dr. Niall Palfreyman 12/9/2006 
Flows (was Feedback Loops) - John Gunkler 2/9/2006
Flows (was Feedback Loops) - Bill Braun 2/9/2006
Feedback Loops - Fernando Mazzuli 2/9/2006 
Feedback Loops - Levin, Jeffrey S. 2/9/2006
Feedback Loops - David Lymburner 2/9/2006
Feedback Loops - John Sterman 2/9/2006
Feedback Loops - Bill Braun 2/9/2006
Feedback Loops - Elane V. Scott 2/8/2006
Feedback Loops - David Lymburner 2/9/2006