The Nature of Equilibria (SL IB Environmental Systems & Societies (ESS))

• An equilibrium refers to a state of balance occurring between the separate components of a system
• Open systems (such as ecosystems) usually exist in a stable equilibrium
  • This means they generally stay in the same state over time
  • They can be said to be in a state of balance
  • A stable equilibrium allows a system to return to its original state following a disturbance

Stable Equilibria

• The main type of stable equilibrium is known as steady-state equilibrium
  • A steady-state equilibrium occurs when the system shows no major changes over a longer time period, even though there are often small, oscillating changes occurring within the system over shorter time periods
  • These slight fluctuations usually occur within closely defined limits and the system always return back towards its average state
  • Most open systems in nature are in steady-state equilibrium
  • For example, a forest has constant inputs and outputs of energy and matter, which change over time
  • As a result, there are short-term changes in the population dynamics of communities of organisms living within the forest, with different species increasing and decreasing in abundance
  • Overall, however, the forest remains stable in the long-term

Photo by Rodion Kutsaiev on Unsplash 

A patch of sky can be considered a steady state if the amount of cloud cover remains the same. The rate of formation and dispersion of clouds is equal, but the system is open as air flows in and out of our view

• Another type of stable equilibrium would be static equilibrium
  • There are no inputs or outputs (of energy or matter) to the system and therefore the system shows no change over time
  • No natural systems are in static equilibrium - all natural systems (e.g. ecosystems) have inputs and outputs of energy and matter
  • Inanimate objects such as a chair or desk could be said to be in static equilibrium

Static and steady-state equilibria are both types of stable equilibria

Stable vs Unstable Equilibria

• A system can also be in an unstable equilibrium
  • Even a small disturbance to a system in unstable equilibrium can cause the system to suddenly shift to a new system state or average state (i.e. a new equilibrium is reached)

A system can be in a stable equilibrium or an unstable equilibrium