Two lessons ago you finished the content of this sub-unit with resilience: why a shallow lake tips, why the prairie blew away in the 1930s, and why Lac Léman is slow to recover. Last lesson you caught up on anything you had missed. This lesson brings back the whole sub-unit, from what a system is to how people make one less resilient. There is no new content, and you will work mostly from memory. By the end you should be able to draw a systems diagram with named storages and flows, say whether a system is open or closed and why, draw feedback loops that close, judge whether a system can come back from a tipping point, and tell resilience apart from stability.
This is the shape of the whole sub-unit.
flowchart TD
A["A system: storages and flows inside a boundary"] --> B["Open or closed, depending on what crosses the boundary"]
A --> C["Feedback loops"]
C --> D["Negative feedback counteracts change"]
C --> E["Positive feedback amplifies change"]
D --> F["Stable equilibrium"]
E --> G["Tipping point"]
G --> H["Regime shift to a new stable state"]
I["Diversity and large storages, which people can reduce"] --> J["Resilience"]
J -->|"keeps a system away from"| G
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1. Dump. Nothing open except this page, and do not open the checkpoint yet. Type everything you can remember under the dump prompt: bullet points, chains of arrows, half-remembered fragments. Do not stop to check anything.
2. Compare. Turn to a partner. Add anything they had that you did not, in a different text colour, so you can see the difference later.
3. Check. Open the checkpoint. Correct what is wrong, again in a different colour, and highlight anything that was missing altogether.
4. Apply. Answer the task at the end of the round, then open Check your answer. The marks in square brackets tell you how much to write.
There are four rounds. If you finish early, try the extension at the end, which pulls the whole sub-unit together in one lake.
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1.2.1 Systems are sets of interacting or interdependent components.
System components are organized to create a functional whole.
1.2.2 A systems approach is a holistic way of visualizing a complex set of interactions, and it can be applied to ecological or societal situations.
A system has storages and flows, with flows providing inputs and outputs of energy and matter.
1.2.3 In system diagrams, storages are usually represented as rectangular boxes and flows as arrows, with the direction of each arrow indicating the direction of each flow.
Application of skills: Create systems diagrams representing the storages and flows, inputs and outputs of systems, such as a lab-based or local natural ecosystems. The size of the boxes and the arrows may be representative of the size/magnitude of the storage or flow.
1.2.4 Flows are processes that may be either transfers or transformations.
Transfers involve a change in location of energy or matter; transformations involve a change in the chemical nature, a change in state or a change in energy.
1.2.5 Systems can be open or closed.
An open system exchanges both energy and matter across its boundary, while a closed system exchanges only energy across its boundary. Almost all systems are open; only the global geochemical cycles approximate to closed systems. Biosphere 2 is an example of a closed system, and a local ecosystem is an example of an open system.
1.2.6 The Earth is a single integrated system encompassing the biosphere, the hydrosphere, the cryosphere, the geosphere, the atmosphere and the anthroposphere.
James Lovelock’s Gaia hypothesis is a model of the Earth as a single integrated system. The hypothesis (also known as the Gaia theory) was introduced to explain how atmospheric composition and temperatures are interrelated through feedback control mechanisms. Many variations of the Gaia theory were further developed by James Lovelock and Lynn Margulis.
1.2.7 The concept of a system can be applied at a range of scales.
Systems are at a range of scales, including a small-scale local ecosystem, such as a bromeliad in a rainforest; a large ecosystem, such as a rainforest; and the Gaia hypothesis or atmospheric circulation as an example of a global system.
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Dump everything you can remember about systems. What makes something a system, what storages, flows, inputs and outputs are, how a systems diagram is drawn, and the difference between a transfer and a transformation, with an example of each. Then the difference between open and closed systems, what Biosphere 2 was and why its oxygen fell, the six spheres, what the Gaia hypothesis claims, and how changing the scale changes what counts as an input.
⛳ Checkpoint (open after you have compared)
Each autumn, leaves fall from the beech trees on the Jura and pile up on the ground as leaf litter. Earthworms, fungi and bacteria break the litter down, releasing mineral nutrients into the soil. Rain soaks into the soil and is held there as soil water, and the trees' roots take up the water and the dissolved nutrients.
1. Construct a systems diagram for the soil system under this forest, including two storages and two flows. Label each flow as a transfer or a transformation. [3]
Type it as one flow per line, with each storage in bold as if it were a box, for example: Algae → grazing (transfer) → Herbivores. If you would rather draw it on paper, photograph it and paste the photo here.