1.2 Systems
When we consider systems we are actually thinking about three interrelated concepts, 1) a theory that provides us with a tool for holistic analysis, 2) a system as an organising structure and 3) complex systems which are further models to show how many different systems are connected together with synergetic emergent properties.
In this section we provide support to understand these three ideas together with the connecting ideas of levels of organisation and scale, feedback loops, resilience and tipping points.
How can the systems approach be used to model environmental issues at different levels of complexity and scale?
Systems theory is a tool to help look at the holistic nature of a system such as the function of a natural system or the mechanics and purpose of a human constructed system. Traditionally, the study of science has broken down systems in a reductionist manner in order to simplify their study, e.g. what does a wolf eat? In a holistic approach, it is not just the wolf that is studied but all its prey, the interactions of those organisms in the entire food web, the feedback relationships between the organisms and the impact they have on their environment. This allows leverage points to be identified in the system, possible tipping points and thus management strategies that might be worthy of trialling.
Systems theory can help in the study of socio-ecological systems by providing conceptual models that help with the analysis of these complex issues, for example, allowing perspectives to be used as lenses for a system.
A system is a set of interacting or interdependent components producing a functional whole that together produce emergent properties. On their own, the components do not produce these properties. Examples include how predator-prey relationships can oscillate (the numbers of predators and prey change as a result of each other) and trophic cascades where a change in one part of the food web creates a cascade of changes throughout the food web and even beyond into the ecosystem.
System Boundaries
In order to study a system, one must first define its boundaries as systems can greatly vary in scale.
Systems operate within boundaries which can be defined. The boundary defines the limits within which the components interact, and thus it defines the scale of the system and the way in which systems are related together. These are human constructs and thus simplifications of the world.
Environmental Systems are physical systems with physical boundaries. Some boundaries are sharp, such as coastlines or a lake shore, or a frontal weather system, which marks the boundary between warm and cold air masses. Other boundaries are less sharp and more transitional, such as the gradual change in vegetation towards a desert margin.
In this image (CC BY-SA 4.0) we see the three aqueducts that supply the water of Southern California. This watershed is a system on a regional scale with boundaries that can be defined by the water that enters these aqueducts.
Scale of Systems
The Earth itself is a very large system with its boundaries defined by the atmosphere surrounding it but also encompassing the biosphere, the hydrosphere, the cryosphere, the geosphere and the anthroposphere.
Biosphere: the part of the earth where living organisms (life) exists
Atmosphere: the layer of air surrounding the Earth’s surface
Hydrosphere: the layer of water on and near the Earth’s surface (this includes the frozen water)
Cryosphere: the layer consisting of frozen water, including frozen ground
Geosphere: the layer that includes all the rocks and minerals from the centre of the Earth to the non-living parts of the soil
Anthroposphere: encompasses the total human presence throughout the Earth system including our culture, technology, built environment, and associated activities[1]
Global Scale Systems
Regional Scale Systems
Small Scale Systems
A bromeliad in a cloud rainforest acts as a small ecosystem for other organisms. A garden pond is a small scale system.
The Gaia Hypothesis is an example of a planetary sized system.
James Lovelock developed his Gaia hypothesis during the 1970s publishing several books and papers on the topic. The Gaia hypothesis proposes that the Earth functions as a living system, having a homeostatic mechanism which regulates conditions on the planet. It was introduced to explain how atmospheric composition and temperatures are interrelated through feedback control mechanisms. There are many variations of the Gaia theory as further developed by James Lovelock and Lynn Margulis.
The hypothesis is useful when thinking about the Earth as a system and particularly in view of the global changes occurring today. Several eminent scientists such as Richard Dawkins don't agree with Lovelock's proposals but others would argue that it is a useful way of debating the global system with feedback mechanisms maintaining an equilibrium.
You can read more about the Gaia Hypothesis at this Harvard Wikipedia Page which opens a pdf file.
As part of the supporting evidence for the Gaia hypothesis, Lovelock developed a computer simulation with Andrew Watson called Daisyworld. This model demonstrates how emergent properties can develop from the interaction between non-living and living components of a system. Feedback loops develop to maintain a constant environment.
To read more about Daisyworld try here.
Here’s James Lovelock talking about the model:
And here's an explanation of his model:
If you like playing with computer models try: NetLogo from Northwestern University and this activity: 1.3: Daisyworld activities.
Systems can be open on closed and are defined by whether energy and or matter cross their boundaries.
An open system exchanges both energy and matter across its boundary and almost all systems are open. An natural ecosystem is an open system, e.g. your local wood or lake.
A closed system exchanges only energy across its boundary. The global geochemical cycles approximate to closed systems. Biosphere 2 is an example of a closed system.
This TED Talk from Jane Poynter talks about her experiences in Biosphere 2 and what that information could be used for in the future (about 15 minutes).
A system has stores and flows, with flows providing inputs and outputs of energy and matter. These flows can move in and out of a system (if open), crossing the system boundary or they can be internal to the system.
inputs: import material and energy across the system boundary
outputs: export material and energy across the system boundary
flows: flows and pathways within the system along which the energy and materials pass – can be transfers or transformations
stores: storage areas within the system where energy and material can be stored for various lengths of time before being released back into the flows
In system diagrams, stores are usually represented as rectangular boxes and flows as arrows, with the direction of each arrow indicating the direction of each flow. The size of the boxes and the arrows may be representative of the size or magnitude of the storage or flow.
Simplified system diagram of a forest:
In this simplified system diagram of a forest, there are inputs and outputs of energy and matter. The boxes represent the stores in the system and the arrows represent the flows both in and out of the systems and within the system but as it is a model it does not represent all the complexity in the system.
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.
System Diagram of Water Cycle:
In the diagram of the water cycle,transformations are marked with a yellow dot. The purple dots represent transfers.
This video (c. 5 minutes) is from Dartmouth College and Prof. Andrew Friedland. He talks you through some very clear examples of feedback loops in the climate.
Negative feedback loops occur when the output of a process inhibits or reverses the operation of the same process in such a way as to reduce change.
- They are stabilising as they counteract deviation.
- They 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.
- It suppresses system changes promoted by external factors.
- This self-regulation is homeostasis and explains stability in systems.
- As an open system, an ecosystem will normally exist in a stable equilibrium, either in a steadystate equilibrium or in one developing over time (for example, succession), and will be maintained by stabilizing negative feedback loops.
An example of a negative feedback loop is a predator-prey interaction.
Positive feedback loops occur when a disturbance leads to an amplification of that disturbance, destabilizing the system and driving it away from its equilibrium.
- Positive feedback can lead to both an increase or a decrease in a system component. For example, as a population declines, the reproductive potential decreases leading to further decrease.
- Positive feedback loops will tend to drive the system towards a tipping point.
An example of positive feedback is the reduced albedo (amount of reflection by a surface) due to melting ice caps leading to greater global warming, or an increase in population leading to increased potential for further growth.
Equilibrium in a System
Open systems are usually in a state of equilbrium; their inputs are being balanced with their outputs.
A steady state equilibrium is the condition of a system in which there is a tendency for it to return to the previous equilibrium following disturbance.
An equilibrium can also develop over time, for example in succession (change in a system over time) and will be maintained by stabilising negative feedback loops. As the system approaches the climax community then the equilibrium approaches a steady state.
Succession is thought to be able to result in many alternative stable states depending upon stocastic differences, i.e. the climax community may be slightly different depending upon the inputs during the process of succession.
Emergent Properties
Interactions between components in systems can generate emergent properties. This means that individually components of a system would act in one way but when the system components come together, there is synergy, the emergent properties interact and a new pattern will emerge. Succession and trophic cascades result in the chance events and interactions between species that emerge as the system develops. These emergent properties would not be observed without these interactions.
Tipping Points
A tipping point is the minimum amount of change that will cause destabilization within a system. The system then shifts to a new equilibrium or stable state.
Tipping points can exist within a system where a small alteration in one component can produce large overall changes, resulting in a shift in equilibrium. Tipping points result in regime shifts between alternative stable states.
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The diagram shows this movement between two alternative states. This would be a regime shift.
- Both states are in an equilibrium but the the conditions may be very different in each state. The location is the same.
- Inputs are received to the system and negative feedback loops may counteract these inputs and return the system to its original equilibrium.
- Inputs may also start a positive feedback loop where by the changes are amplified.
- Beyond a certain point, a tipping point is reached, and the system moves to a new alternative state in a new equilibrium.
Tipping points can be the result of the re-introduction of a species. In this case we call them trophic cascades and they are positive for the stability and resilience of the system.
Tipping Points are more generally thought of as disastrous such as in the climate change positive feedback loops.
Application of Skills:
Use diagrams representing examples of positive feedback.
Resilience, diversity and stability of a system are intrinsically linked. Resilience is the capacity of a system, whether ecological or social, to resist change, to resist, recover from or adapt effectively to disturbance. By having sufficiently large stores and diversity (a complex set of interactions) the resilience of a system can avoid tipping points and maintain stablility.
In the picture to the left, we see Brazilian rainforest that has been experimentally set up to have difference sizes of plots (stores) surrounded by deforestation. The forest fragments project[2], since 1979, has monitored 94 hectares (232 acres) of forest plots. Every five years, the project conducts a tree census, tagging, collecting data on, and cataloging every tree larger than 10 cm in diameter. The data is then compiled into a database. Many conclusions can be made from this research but put simply, the smaller the area (the smaller the stores), the less resilient that area is to rare events such as extreme weather events. So in this case, humans, through their actions of deforestation, reducing the size of the stores and the diversity, have reduced the resilience of the system. Other conclusions[3] include:
- many rainforest species are naturally rare and hence are either missing entirely from many fragments or so sparsely represented as to have little chance of long-term survival
- edge effects (the smaller the area, the bigger the edge) are a prominent driver of fragment dynamics, strongly affecting forest microclimate, tree mortality, carbon storage and a diversity of fauna
- the most locally extinction-prone animal species are those that have both large area requirements and low tolerance of the modified habitats surrounding fragments
- the most vulnerable plants are those that respond poorly to edge effects or chronic forest disturbances, and that rely on vulnerable animals for seed dispersal or pollination
- global and regional drivers of change are also impacting the community composition, making some species more abundant than previously, e.g. tree lianas.
Watch this video (c. 8 minutes) to understand the interrelationship between species and forest fragmentation and how ecologists go about their research and why.
Climate also affects the resilience of a system. In this image, the ring in the sedge-tussock tundra was taken in 2005 but is the result of a camp in 1984. In cold and seasonally dark climates, plants are not able to photosynthesise as rapidly as those in warmer climates and do the resilience of the system and the speed of response to change (time lags) is much slower. In these systems diversity is low and this does not provide multiple opportunities to respond to change.
When European colonisers moved west across North America they found large areas of prairies (that had co-existed with the indigenous first nations people of America) that appeared ideal for cultivation. The land was ploughed and planted with monocultures (one species) of grain crops such as wheat. This reduced the diversity of the system and the store of the soil carbon (prairie plants have much of their biomass in the soil).
When drought hit in the 1930s, the system had a reduced resilience and vast areas of top soil were lost from the system preventing the area being farmed again. This was called the dust bowl and led to government led changes to the land management with farmers being paid to return the land to prairies. When the system had reduced stores of soil and carbon, the system was not able to respond to change (drought). Even the recovery of the land was slow due to these reduced stores.
These two system diagrams show the comparative size of a store in a puddle (small pool of water forming temporarily after rain - it is ephemeral) and a lake. The size of the stores is represented by the size of the boxes. Evaporation is a flow out of both systems but has a much bigger effect on the puddle as it is much less resilient due to the store being so much smaller.
Humans affect the resilience of systems by reducing the size of stores and reducing diversity as can be seen in the examples of deforestation and the dustbowl of the American mid-West.
A model is a simplified representation of reality. The image is a model of the Earth. It is a representation of the balance in land to ocean but has been constructed to serve a purpose, it helps us understand the earth system but it is a simplification and has biases built into it based on the time and place of the model builder. It is an appromiximation and therefore has a loss of accuracy.
There are many types of models and we use them a lot in ESS.
Systems diagrams represent the stores and flows in a system. They may contain numerical information such as the size of the store and the size of the flow but they will often focus on a simplified version of a system. This helps us but also loses information through the simplification.
In ecology, food chains, food webs and ecological pyramids are all models of a system showing the numbers, biomass, energy flow in an ecosystem.
The global biogeochemical cycles are represented as flow charts with stores and flows representing the processes taking place such as photosynthesis in the carbon cycle or nitrogen fixation by lightning in the nitrogen cycle.
In climate change, scientists use algorithms (mathematical equations) in their models to predict how the climate will respond to different scenarios of change. These can be mapped backwards to check their viability with existing data. Human population demographers also use models to make predictions about human population growth changes.
Simulations are also models of a system that help us understand what may be happening in reality. The Daisy World Simulation helps us understand the nature of feedback loops as do predator-prey simulations.
Scientists often simplify systems to study them. We do this when we devise lab experiments to model what might be happening on a system level. Ecologists, though, often use data from actual systems to build models and interpret what they observe.
In our classrooms we often use models to help visualise our thinking, representing our metacognition.
• Build a bottle ecosystem, aquarium, terrarium, compost heap or other school-based ecosystem and use it to construct a systems diagram. Compare variables of the system (for example, with and without one organism or with different levels of water/nutrients.)
• Use the skills of system analysis to help solve a whole-school problem.
• Advocate to peers to educate them about the importance of tipping points.
Footnotes
- ^ https://www.agci.org/earth-systems/anthroposphere retrieved 19/2/23
- ^ https://www.amazonbiodiversitycenter.org/programs-and-projects
- ^ https://onlinelibrary.wiley.com/doi/abs/10.1111/brv.12343