Feedback Loops

Ecosystem feedback is the effect that change in one part of an ecosystem has on another and how this effect then feeds back to affect the source of the change inducing more or less of it.  These feedback loops form the basic dynamics for regulating the state of the ecosystem.

A negative feedback loop is where the state of one element affects the other in the opposite direction, with the net result of this being a stable system where different forces are counterbalancing each other out creating some equilibrium

Positive feedback stimulates change and it is responsible for the sudden appearance of rapid changes within ecosystems. Positive feedback is a circular link of effects that are self-reinforcing. When part of the system increases, another part of the system also changes in a way that makes the first part increase even more. Positive feedback is a source of instability and strong force of change as it can drive the system outside of its normal operating parameters.

Positive Feedback Loop Examples

The melting of the polar ice caps is an example of a vicious cycle, as the reflective ice caps melt they reflect less sunlight and heat back to the atmosphere, with more of this heat being trapped by the dark ocean which is now exposed by the loss of ice cap. This retained heat then increases the temperature feeding back to induce the melting of more ice caps creating what we would call a vicious circle.

We might cite the pollution of the lagoons that surround small South Pacific islands. Many South Pacific communities now consume imported packaged and canned foods, disposing of the empty cans and other waste in dumps. Rainwater runoff from the dumps pollutes the lagoons, reducing the quantity of fish and other seafood. With less seafood, people are forced to buy more and more cheap canned food, the pollution becomes worse and the lagoon has fewer fish. This positive feedback loop changes the lagoon ecosystem while also degrading the people’s diet again creating a vicious circle.

Negative Feedback Loop Example

Look at the succession of an ecosystem from grass to shrub community, beginning with an ecosystem in which the ground is covered with grasses. Shrubs may be present, but they are young and scattered. The ecosystem may stay this way for five to ten years, or possibly longer, because shrub seedlings grow very slowly. They grow slowly because grass roots are located in the topsoil, while most of the shrub roots are lower down. Grasses intercept most of the rainwater before it reaches the roots of the shrubs. Because the grasses limit the supply of water to the shrub seedlings, they maintain the integrity of the ecosystem as a grass ecosystem. At this stage, negative feedback is acting to keep the biological community the same.

Various sources used for this post

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