The document discusses the laws of thermodynamics and their implications for ecological systems, emphasizing energy conservation, entropy, and system stability. It explains the concepts of feedback loops, tipping points, and resilience within ecosystems, highlighting how these factors influence the ability of a system to maintain equilibrium. The document also addresses human impacts on ecosystem resilience and the challenges in predicting tipping points due to feedback delays.

1. 1.3 Energy and equilibria
Monday, October 26, 2015
Scott Lucas
Dwight School London, 2015

2. Assessment statements
Significant ideas
• The laws of thermodynamics govern the flow of
energy in a system and the ability to do work.
• Systems can exist in alternative stable states or as
equilibria between which there are tipping points.
• Destabilizing positive feedback mechanisms will
drive systems toward these tipping points, whereas
stabilizing negative feedback mechanisms will resist
such changes.

3. Assessment statements
Knowledge and understanding
[The use of examples in this sub-topic is particularly important so that the
abstract concepts have a context in which to be understood.]
• The first law of thermodynamics is the principle of conservation of
energy, which states that energy in an isolated system can be
transformed but cannot be created or destroyed.
• The principle of conservation of energy can be modelled by the energy
transformations along food chains and energy production systems.
• The second law of thermodynamics states that the entropy of a system
increases over time. Entropy is a measure of the amount of disorder in a
system. An increase in entropy arising from energy transformations
reduces the energy available to do work.
• The second law of thermodynamics explains the inefficiency and
decrease in available energy along a food chain and energy generation
systems.

4. Assessment statements
Knowledge and understanding
• As an open system, an ecosystem will normally exist in a stable
equilibrium, either in a steady-state equilibrium or in one developing
over time (for example, succession), and maintained by stabilizing
negative feedback loops. [A stable equilibrium is the condition of a
system in which there is a tendency for it to return to the previous
equilibrium following disturbance.] [A steady-state equilibrium is the
condition of an open system in which there are no changes over the
longer term, but in which there may be oscillations in the very short
term.]
• Negative feedback loops (stabilizing) occur when the output of a process
inhibits or reverses the operation of the same process in such a way as
to reduce change—it counteracts deviation.
• Positive feedback loops (destabilizing) will tend to amplify changes and
drive the
system toward a tipping point where a new equilibrium is adopted.

5. Assessment statements
Knowledge and understanding
• The resilience of a system, ecological or social, refers to its tendency to
avoid such tipping points and maintain stability. [Emphasis should be
placed on the relationships between resilience, stability, equilibria and
diversity.]
• Diversity and the size of storages within systems can contribute to their
resilience and affect their speed of response to change (time lags)
• Humans can affect the resilience of systems through reducing these
storages and diversity.
• The delays involved in feedback loops make it difficult to predict tipping
points and add to the complexity of modelling systems. [A tipping point
is the minimum amount of change within a system that will destabilize
it, causing it to reach a new equilibrium or stable state.] [Examples of
human impacts and possible tipping points should be explored.]

6. Assessment statements
Applications and skills
• Explain the implications of the laws of thermodynamics
to ecological systems.
• Discuss resilience in a variety of systems.
• Evaluate the possible consequences of tipping points.
International-mindedness
• The use of energy in one part of the globe may lead to
a tipping point or time
lag that influences the entire planet’s ecological
equilibrium.

7. Vocabulary
• First law of thermodynamics: energy in an isolated system can be transformed but
cannot be created or destroyed
• Second law of thermodynamics: energy is transformed through energy transfers
which increases entropy that reduces the energy available to do work
• Entropy: a measure of the amount of disorder in a system
• Equilibrium: the tendency of a system to return to an original state following a
disturbance
• Static (stable) equilibrium: no change over time; will adopt a new equilibrium if
disturbed – non-living systems
• Steady-state (dynamic) equilibrium: the system as a whole remains more-or-less
constant, even with continuous inputs and outputs of matter and energy
• Stable: system returns to the same equilibrium after a disturbance
• Unstable: system returns to a new equilibrium after a disturbance
• Negative feedback loop: when the output of a process inhibits/reverses the process
to reduce change – it counteracts deviation “stabilizing”
• Positive feedback loop: tends to amplify change toward a tipping point where a new
equilibrium is adopted – destabilizing
• Resilience: the ability of a system to return to its initial state after a disturbance
• Tipping point: the critical point in a situation, process, or system beyond which a
significant and often unstoppable effect or change takes place

8. SI1.3.1 The laws of thermodynamics
govern the flow of energy in a system
and the ability to do work
• Energy in all systems is subject to the laws of
thermodynamics

9. U1.3.1 The first law of thermodynamics is a principle of
conservation of energy, which states that energy in an isolated
system can be transformed but cannot be created or destroyed
• Total energy of an isolated system, i.e. the universe,
is constant
• The form of energy can change though
• Light (sunlight) energy to heat (radiation) energy
• Chemical energy (fossil fuels) to electrical energy

10. U1.3.1 The first law of thermodynamics is a principle of
conservation of energy, which states that energy in an isolated
system can be transformed but cannot be created or destroyed

11. U1.3.2 The principle of conservation of energy can be
modelled by the energy transformations along food
chains and energy production systems
Learn the specific
organisms in this
example of a food
chain

12. U1.3.3 The second law of thermodynamics states that the entropy of a
system increase over time. Entropy is a measure of the amount of disorder
in a system. An increase in entropy arising from energy transformations
reduces the energy available to do work.
• More entropy = less order
• Over time the thermal death of the universe will be
reached, energy differences will be evened out until
nothing can change
• Energy conversions are never 100% efficient
• When energy is used to do work, some energy is
always lost as heat

13. Entropy
• High quality energy such as light (via photons) and
chemical energy (via bonds between atoms) can be
used to do work = ordered = low entropy
• Low-quality energy, heat cannot be used to do
work (or very little) = disordered = high entropy
• Over time high-quality energy (low entropy)
degrades to low-quality energy (high entropy) =
entropy increases
• Ex. light  chemical  mechanical  heat

14. U1.3.4 The second law of thermodynamics explains
the inefficiency and decrease in available energy
along a food chain and energy generation systems.

15. • Energy is lost between each trophic level in a food
chain/web
• Plants are 1-2% efficient converting insolation (solar
energy) into sugar (chemical energy)
• Herbivores assimilate (turn into animal matter) ~10% of
the total energy they consume
• The rest is metabolism (respiration), movement, heat, fecal
matter,
• Carnivores is ~10% efficient
• Used for respiration, movement, heat
• Shed skin/antlers & bones aren’t consumed typically so aren’t
passed from the herbivore trophic level

16. Calculating efficiency
• Efficiency: amount of useful energy/work/output
divided by the amount of energy consumed/input
into the process
• Efficiency =
output (work produced or useful energy)
input (energy consumed)
• % Efficiency =
useful output
input
* 100%

17. Summary of second law

18. S1.3.1 Explain the implications of the laws of
thermodynamics to ecological systems
• First?
• Second?

19. S1.3.1 Explain the implications of the laws of
thermodynamics to ecological systems
• First
• Energy is transferred/transformed but not destroyed
• Energy is converted from one form to another, eventually
ending up as heat
• Second
• Living systems tend to disorder
• Energy is required to maintain or increase order
• This requires a source of energy, the sun or food, to continue
to remain ordered
• Energy transfer is never 100% efficient so some energy is lost
as heat
• Energy transfer is about 10% efficient between trophic levels

20. SI1.3.2 Systems can exist in alternative stable
states or as equilibria between which there are
tipping points
• More complex systems are more likely to be stable
and withstand stress/change better
• Ecosystems follow this; more complex ones i.e.
more organisms at each trophic level result in a
more stable system, it can withstand stress and
change better
• Analogy: a road network with one road connecting
two points
• If that road gets blocked then you cannot reach your
destination
• If there are other roads then you can take another route

21. SI1.3.2 Systems can exist in alternative stable states
or as equilibria between which there are tipping
points
• Tundra is a simple ecosystem; if something happens
populations can vary widely e.g lemmings
• Monocultures; farm only one crop, if disease/pests
attack they destroy the whole crop
• Ex. potato blight in Ireland 1845-8

22. Equilibrium
• The tendency of a system to return to an original state
following a disturbance
• Equilibriums moderate changes in a system, preventing
sudden drastic changes; keeping change between limits
• Can think of systems in terms of
• Activity
• Steady-state (dynamic): the system as a whole remains more-or-
less constant, even with continuous inputs and outputs of matter
and energy – living systems
• Static (stable): no change over time; will adopt a new equilibrium if
disturbed – non-living systems
• Stability
• Stable: system returns to the same equilibrium after a disturbance
• Unstable: system returns to a new equilbirum after a disturbance

23. Activity: Steady-state examples
• Water tank that fills and empties at the same rate; there is
activity but no change in the overall water level
• Economics, stable market even with flows of capital in and
out
• Ecology, population size may stay the same even with births
and deaths occurring, no net change
• Body temperature, fluctuates but remains around 37 °C;
cold – shiver to warm up, hot – sweat to cool down

24. Activity: Static examples
• A pile of books will remain until knocked over, the
new equilibrium
• Buildings remain the same for a long time i.e. don’t
move/change position

25. Stability
Stable
Unstable

26. Feedback loops
• Systems receive information from outside and inside the
system
• The system reacts to this information and either stabilizes
(negative feedback) or changes (positive feedback) the
system
• Ex. You feel cold (information) so you but a sweater on or
turn up the heat (reaction)
Ex. You feel hungry (information) so you eat food (reaction)
or get hungrier (increasing in information strength)
• Negative: returns to original state by counteracting change
• Positive: changes system to new state by
destabilizing/increasing change

27. U1.3.5 As an open system, an ecosystem, will normally exist in a stable equilibrium,
either a steady-state or one developing over time (eg succession), and maintained
by stabilizing negative feedback loops
U1.3.6 Negative feedback loops (stabilizing) occur when the output of a process
inhibits or reverses the operation of the same process in such a wat to reduce
change – it counteracts deviation
• Negative feedback loop: when the output of a process
inhibits/reverses the process to reduce change – it
counteracts deviation “stabilizing”
• Negative feedback prevents change which helps
maintain ecosystem’s steady-state equilibria
• Systems are self-regulated by negative feedback
mechanisms
• Short term changes may happen but long term the
system is steady-state
• Succession is development of an ecosystem’s stability
over time

28. Negative feedback examples

29. Negative feedback examples
• Body temperature: you are exercising, your body
temperature rises, detectors in you body sense the
increase, your body starts to sweat and blood flow
to the surface of you skin increases, these help cool
you down
Simple predator prey interactions:
prey increase, more food for
predators; predators increase, eat
more prey; prey numbers drop,
due to more predators; predator
numbers drop due to less prey
(food), etc

30. Predator-prey negative feedback

32. SI1.3.3 Destabilizing positive feedback mechanisms will drive systems toward these
tipping points, whereas stabilizing negative feedback mechanisms will resist such
change
U1.3.7 Positive feedback loops (destabilizing) will tend to amplify changes and drive
the system toward a tipping point where a new equilibrium is adopted
• Positive feedback loop: tends to amplify change
toward a tipping point where a new equilibrium is
adopted – destabilizing
• Amplifies the system output which leads to further
change
• Eventually the deviation from equilibrium is too
much and a new equilibrium is established
• A “vicious circle”

33. Examples of positive feedback

34. Examples of positive feedback
• Body temperature: lost high up on a snowy
mountain, body shivers to warm up, doesn’t work
so metabolism slows, you become lethargic and
sleepy, move less, body cools more, hypothermia,
death; unless you are saved
• Task: Feedback mechanism worksheet

35. U1.3.8 The resilience of a system, ecological or
social, refers to its tendency to avoid such
tipping points and maintain stability
• Resilience: the ability of a
system to return to its initial
state after a disturbance
• High resilience = return to
equilibrium
• Low resilience = enter a new
state/equilibrium
• Resilience is usually good but
can be bad
• Ex. antibiotic resistant
bacterial are resilient to
antibiotics, good for them,
bad for us

36. U1.3.9 Diversity and the size of storages within
systems can contribute to their resilience and affect
the speed of response to change (time lags)
• Factors affecting ecosystem resilience
• High diversity/complex, more interactions between species =
more resilience
• Greater species biodiversity, more likely one species can
replace another = more resilience
• Greater genetic diversity within a species, allows different
traits = more resilience
• Species with wider ranges = more resilience
• Larger ecosystems, less edge effect, more space to move
around = more resilience
• Climate; cold slows photosynthesis and growth = less
resilience; hot increases growth (condition dependent) =
more resilience
• Faster reproductive rate = more resilience

37. U1.3.10 Humans can affect the resilience of
systems through reducing these storages and
diversity
• Factors affecting ecosystem resilience
• Humans: can remove or mitigate the threat ex.
pollution, invasive species, etc = more resilience
• Humans: can reduce size of storages by harvesting;
wood, fish, etc
• Humans: can reduce diversity by species extinction =
less resilience

38. S1.3.2 Discuss resilience in a
variety of systems

39. U1.3.11 The delays involved in feedback loops
make it difficult to predict tipping points and add
to the complexity of modelling systems
• Within limits an ecosystem can recover and re-establish
its equilibrium
• When the disturbance is too great, the ecosystem
reaches a tipping point
• Tipping point: the critical point in a situation, process,
or system beyond which a significant and often
unstoppable effect or change takes place (Merriam-
Webster)
• Past the tipping point the ecosystem cannot re-
establish its equilibrium
• Positive feedback pushes the ecosystem to a new
equilibrium where there are significant changes to
biodiversity and services it provides

40. U1.3.11 The delays involved in feedback loops
make it difficult to predict tipping points and add
to the complexity of modelling systems
• Characteristics of a tipping point
• Involves positive feedback that leads to self-
perpetuation eg. Deforestation reduces rainfall,
increased fire risk, forest dieback
• There is a threshold past which a fast shift of ecological
states occurs
• The threshold point cannot be precisely predicted
• Changes are hard to reverse
• Significant lag time between the pressures driving the
change and the appearance of impacts, this creates
great difficulties in ecological management (i.e. we can’t
see the damage until it is far along)

41. U1.3.11 The delays involved in feedback loops
make it difficult to predict tipping points and add
to the complexity of modelling systems
• Examples
• Eutrophication: nutrients build up, plants flourish,
dissolved oxygen (DO) drops, animals die, bacteria
decompose organic matter, reduces DO further
• Keystone species extinction: keystone species is
required to maintain equilibrium otherwise an
irreversible shift occurs to a new state, elephant in
savannah
• Coral reef death: ocean acidity rises, coral reef dies and
cannot regrow
• Climate change: might be reaching a global tipping point
where our climate ends up to 8 °C warmer due to
human activities

42. S1.3.3 Evaluate the possible
consequences of tipping points
• If there is a global tipping point consequnces could
include
• Not being able to respond quick enough
• Inaction or despair
• Precautionary may be best; we don’t know what
will happen so we should prevent it from changing
as much as possible

43. Visit ProjectEd for more resources
https://sites.google.com/a/dwightlondon.org/projected/

44. Works Cited
• International Baccalaureate Organization. Diploma
Programme Environmental systems and societies guide.
The Hague: IB Publishing Ltd, Feb. 2015. PDF.
• Merriam-Webster. Merriam-Webster, n.d. Web. 15 Aug.
2015. <http://www.merriam-
webster.com/dictionary/>.
• "Modelling with Spreadsheets." BBC News. BBC, n.d.
Web. 13 Aug. 2015.
<http://www.bbc.co.uk/schools/gcsebitesize/ict/model
ling/0spreadsheetsrev5.shtml>.
• Rutherford, Jill. Environmental Systems and Societies.
Oxford: OUP, 2015. Print.