Subject: Feedback Loops

Posted by Prof. Dr. Niall Palfreyman on 12/9/2006
In Reply To:Feedback Loops Posted by Linda Booth Sweeney on 2/8/2006

Message:

I find this example very thought-provoking. First, as John Gunkler says, a feedback loop doesn't just consist of energy-flow, but also of information flow (which of course also ultimately involves energy flow, but I think we usually rightfully neglect this fact). If I reduce the food-chain down to one fox population interacting with one rabbit population, then clearly foxes eat (i.e.: obtain energy from) rabbits, but not the other way around. But what about information flow? Do rabbits signal foxes to stop eating? I guess they do, in a way: when rabbits are scarce, they come in less contact with the foxes, and so the rate of eating slows. Therefore this simple link in the food chain is indeed a feedback loop.

Yet I'm still hung up on Andy Ford's point: are we all using the expression "feedback loop" in the same way here? What reduces the number of rabbits: foxes, maybe? I would say no. A fox doesn't reduce the rabbits, but rather an "eating event", or "eating process", between the fox and rabbit reduces the rabbits. So under this interpretation, the "feedback loop" is not something between foxes and rabbits, but rather between a rabbit and the "eating event", and between a fox and the "eating event". Both rabbit and fox are affected by the event, and both play a part in initiating it. So to my mind this interaction is a combination of two feedback loops: "Fox<->eating" and "Rabbit<->eating", and I view a feedback loop as a relationship between a stock and a process, in which the process changes the stock, and the stock promotes or inhibits the process.

Best wishes,
Niall.

Follow Ups:

Flows (was Feedback Loops) - John Gunkler 2/9/2006 
Flows (was Feedback Loops) - Bill Braun 2/9/2006