This document discusses key concepts in environmental systems and societies, including: 1. Ecosystems can range from small self-contained communities to the entire biosphere of the planet. Biomes are large open ecosystems that span stable climates. 2. The laws of thermodynamics state that energy is conserved but tends towards disorder, so systems seek equilibrium. There are several types of equilibrium including static, steady state, stable, and unstable. 3. Feedback mechanisms can be positive or negative, with negative feedback restoring equilibrium and positive feedback driving a system to a new state. Examples of feedback in maintaining human body temperature are provided.

1. Topic 1
Foundations of Environmental
Systems and Societies
1.3 Energy and Equilibria

2. Ecosystems
• Most of the systems we will look at are
ecosystems (self contained communities of living
things and their surrounding environment)
• Very large ecosystems which span a fairly stable
climate are biomes
• Many biologists say the whole planet is a single
ecosystem (e.g. Gaia Theory). Some of them call
it a CLOSED ecosytem

3. Biomes and Biospheres
• Biome – An open ecosystem in a
geographically defined area with similar
climatic conditions throughout – eg, desert,
grassland (savannah), tropical rainforest
• Biosphere – A closed ecosytem – generally
made up of a range of biomes (i.e. the entire
Earth)

4. A Climograph
Meanannualtemperature(oC)
Rainfall (mm/year)
-15
-10
-5
-0
5
10
15
20
25
1000 2000 3000 4000 5000 6000
desert
grassland Tropical rainforest

5. The Laws of Thermodynamics
• 1st Law:
Energy can neither be created nor destroyed. It is
conserved and transformed from one form to another
• 2nd Law:
Entropy of a system always increases
i.e. energy always changes to a less concentrated, less
useful form, and therefore disorder increases

6. Equilibrium
• A system needs to be in equilibrium
• If not, entropy will increase so much the
system will destroy itself by becoming too
disordered
• There a 4 kinds of equilibrium:
– Static
– Steady State
– Stable
– unstable

7. Static Equilibrium
time
State of the system
Note: this is not realistic – it could only
occur in an isolated system

8. Steady State Equilibrium
time
State of the system

9. Stable Equilibrium
time
State of the system
disturbance
Weebles
wobble but
they don’t fall
down!

10. Unstable Equilibrium
time
State of the system
disturbance
He’s going
down!

11. Feedback Mechanisms
• This is a way that the INPUT is affected by the
OUTPUT
• In a stable equilibrium, feedback returns the
equilibrium to its original state
• In an unstable equilibrium, feedback returns the
equilibrium to a different state
• Feedback can be
– POSITIVE – input changes to bring the system to a new
equilibrium
– NEGATIVE – input changes in order to bring the
system back to its original equilibrium
Positive and negative feedback loops

12. Negative Feedback
• Your (stable) equilibrium body temperature is
37oC
• Sensors in the skin detect your skin
temperature is rising (you are in Cancún)
• Show what happens in a system diagram

13. Positive Feedback
• Your (stable) equilibrium body temperature is
37oC
• Sensors in the skin detect your skin
temperature is decreasing (you are locked in a
freezer)
• Your body is unable to maintain its stable
equibilibrium and therefore you enter a state
of hypothermia
• Show what happens in a system diagram

14. Case Studies
predator-prey equilibria