Transcript 1.1.6 Positive and Negative Feedback

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Living systems display the following 3
characteristics: functionality, sustainability,
evolution.
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The way that living systems and even
inanimate systems self-regulate or maintain
homeostasis (the maintenance of a steady
state in an organism, ecosystem or
biosphere) is through feedback systems
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Negative feedback systems include a
sequence of events that will cause an effect
that is in the opposite direction to the
original stimulus and thereby brings the
system back to its equilibrium position.
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This one illustrates a Balancing Loop or a
negative feedback loop.
•http://www.systemsthinking.org
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Positive feedback includes a sequence of
events that will cause a change in the same
direction as the stimulus and thereby
augments the change, moving the state of
the system even further from the equilibrium
point.
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“James Lovelock argues that such things as the
level of oxygen, the formation of clouds, and the
saltiness of the oceans may be controlled by
interacting physical, chemical and biological
processes. He believes that "the self-regulation of
climate and chemical composition is a process that
emerges from the rightly coupled evolution of
rocks, air and the ocean - in addition to that of
organisms. Such interlocking self-regulation, while
rarely optimal - consider the cold and hot places of
the earth, the wet and the dry - nevertheless keeps
the Earth a place fit for life." The New York Times
Book Review has called his arguments in favor of
Gaia "plausible and above all illuminating."
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Predator/prey relationships are usually
controlled by negative feedback where:
The increase in prey-increase in
predator- decrease in prey decrease in
predatorincrease in prey---and so on in a
cyclical manner. The classic study in
Northern Canada between the Lynx and the
hare populations is famous for its regular
11 year cycle of rising and falling
populations.