Environmental Science For Dummies
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Some ecosystems exist in a steady state, or homeostasis. In steady-state systems, the amount of input and the amount of output are equal. In other words, any matter entering the system is equivalent to the matter exiting the system.

An ecosystem includes living organisms and the environment that they inhabit and depend on for resources. Environmental scientists who study system interactions, or system dynamics, have defined a few important patterns to these interactions.

Some lakes exist as steady-state systems in terms of their water volume. For example, a lake that has a stream feeding water into it may also be losing water that soaks into the ground or exits by another stream.

In this way, even though the stream provides a constant input of water into the lake, the lake also experiences a constant and equal output of water. As a result, the total amount of water within the lake stays the same.

Most systems continually shift inputs and outputs to maintain a steady state. Your body temperature, which remains fairly constant, is one example. When your body gets too hot, it releases heat through sweating. When your body gets too cold, it generates more heat through shivering. In this way, your body attempts to keep your temperature at a steady state by making minor adjustments to its energy inputs and outputs.

Like your body temperature, many natural systems respond to inputs by adjusting outputs. In fact, maintaining a steady state without change is difficult (and rare). So as systems try to reach equilibrium, they constantly shift inputs and outputs.

The adjustments that a system makes as inputs enter or outputs exit are called feedbacks. The two types of feedbacks are

  • Negative feedbacks: These feedbacks slow down or suppress changes, sometimes helping the system return to a steady state.

  • Positive feedbacks: These feedbacks lead to increased change, sending the system further away from a steady state.

Feedbacks often set off a chain of changes, called a feedback loop, in the system. For example, the internal regulation of your body temperature is a negative feedback loop. A change in your body temperature triggers parts of the system (your body) to respond by increasing (shivering) or decreasing (sweating) the temperature and sending it back toward a steady state, thus suppressing change.

On the other hand, population growth can create a positive feedback loop. When more births occur, the next generation has more people to have more babies. In time, these babies grow up to have more babies, who grow up to have more babies, and so on. Thus, positive feedback loops can lead to runaway effects — sending a system far from its steady state.

In the context of systems, the terms positive and negative don’t mean good and bad. In fact, positive feedbacks are often more dangerous than negative feedbacks because they move a system further from stability.

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Alecia M. Spooner teaches Earth and Environmental Sciences at a community college and enjoys developing active-learning science curriculums for adults. Alecia is also the author of Geology For Dummies.

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