Chapter 4 - Introduction to Systems Theory

8/8/2019 Chapter 4 - Introduction to Systems Theory

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Physical Geography Textbook

101 Introduction of System Theory

CHAPTER 4: Introduction to Systems Theory

(a). Humans and Their Models

(b). Definitions of Systems and Models

(c). Structure of Systems

(d). Environmental Systems as Energy Systems

(e). Food Chain as an Example of a System

(f). Equilibrium Concepts and Feedbacks
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(a). Humans and Their Models

One common conclusion of scientific inquiry is that the world of nature is often verycomplex. To understand this complexity, scientists usually try to envisage the phenomena of nature as simplified versions of reality known as a system . A system can be defined as a

collection of interrelated parts that work together by way of some driving process.

In the world of science, the word model is quite similar in meaning to the term system.Models in science tend to be simplified represenations of reality that can be explainedofmathematically and through the use of graphics. The following graphical model is used tohelp explain the processes involved in scientific understanding. The arrows in this graphicallymodel suggest a continuous interaction between perceptible phenomena and theory throughthe processes of explanation and validation . This simple graphical model, while an extremeabstraction of the real world, is quite useful in explaining how scientific understandingworks.

Figure 4a-1 : The general relationship between perceptiblephenomena and theory using scientific method for understanding. The

interaction between perceptible phenomena and theory is arrived atthrough the processes of explanation and validation.

In Physical Geography, and many other fields of knowledge, systems and models are usedextensively as aids in explaining natural phenomena around us.
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(b). Definitions of Systems and Models

As suggested in the previous section, a system is a assemblage of interrelated parts that work together by way of some driving process (see Figure 4b-1 ). Systems are often visualized ormodeled as component blocks that have connections drawn between them. For example, the

illustration below describes the interception of solar radiation by the Earth. In this system, theEarth and Sun, the parts or component blocks , are represented by two colored circles of different size. The process of solar emission and the interception of the Sun's emittedradiation by the Earth (the connection ) is illustrated by the drawn lines.

Figure 4b-1 : Simple visual model of solar radiation being emittedfrom the Sun and intercepted by the Earth.

Most systems share the same common characteristics . These common characteristicsinclude the following:

1. Systems have a structure that is defined by its parts and processes.2. Systems are generalizations of reality .3. Systems tend to function in the same way. This involves the inputs and outputs of

material (energy and/or matter ) that is then processed causing it to change in someway.

4. The various parts of a system have functional as well as structural relationships between each other.

5. The fact that functional relationships exist between the parts suggests the flow and transfer of some type of energy and/or matter .

6. Systems often exchange energy and/or matter beyond their defined boundary with theoutside environment, and other systems, through various input and output processes.7. Functional relationships can only occur because of the presence of a driving force .8. The parts that make up a system show some degree of integration - in other words the

parts work well together.

Within the boundary of a system we can find three kinds of properties :

Elements - are the kinds of parts (things or substances) that make up a system. These partsmay be atoms or molecules, or larger bodies of matter like sand grains, rain drops, plants,animals, etc.

Attributes - are characteristics of the elements that may be perceived and measured. Forexample: quantity, size, color, volume, temperature, and mass.
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Relationships - are the associations that occur between elements and attributes. Theseassociations are based on cause and effect.

We can define the state of the system by determining the value of its properties (theelements , attributes , and/or relationships ).

Scientists have examined and classified many types of systems. Some of the classified typesinclude:

Isolated System - a system that has no interactions beyond its boundary layer. Manycontrolled laboratory experiments are this type of system.

Closed System - is a system that transfers energy, but not matter, across its boundary to thesurrounding environment. Our planet is often viewed as a closed system.

Open System - is a system that transfers both matter and energy can cross its boundary to the

surrounding environment. Most ecosystems are example of open systems.

Morphological System - this is a system where we understand the relationships betweenelements and their attributes in a vague sense based only on measured features orcorrelations. In other words, we understand the form or morphology a system has based onthe connections between its elements. We do not understand exactly how the processes work to transfer energy and/or matter through the connections between the elements.

Cascading System - this is a system where we are primarily interested in the flow of energyand/or matter from one element to another and understand the processes that cause thismovement. In a cascading system, we do not fully understand quantitative relationships that

exist between elements related to the transfer of energy and/or matter.

Process-Response System - this is a system that integrates the characteristics of bothmorphological and cascading systems . In a process-response system, we can model theprocesses involved in the movement, storage, and transformation of energy and/or matterbetween system elements and we fully understand how the form of the system in terms of measured features and correlations.

Control System - a system that can be intelligently manipulated by the action of humans.

Ecosystem - is a system that models relationships and interactions between the various bioticand abiotic components making up a community or organisms and their surroundng physicalenvironment.

(c). Structure of Systems

Systems exist at every scale of size and are often arranged in some kind of hierarchical fashion . Large systems are often composed of one or more smaller systems working withinits various elements . Processes within these smaller systems can often be connected directlyor indirectly to processes found in the larger system. A good example of a system within

systems is the hierarchy of systems found in our Universe . Let us examine this system fromtop to bottom:
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At the highest level in this hierarchy we have the system that we call the cosmos or Universe.The elements of this system consist of galaxies, quasars, black holes, stars, planets and otherheavenly bodies. The current structure of this system is thought to have come about becauseof a massive explosion known as the Big Bang and is controlled by gravity, weak and strongatomic forces, and electromagnetic forces.

Around some stars in the universe we have an obvious arrangement of planets, asteroids,comets and other material. We call these systems solar systems . The elements of this systembehave according to set laws of nature and are often found orbiting around a central starbecause of gravitational attraction. On some planets conditions may exist for the developmentof dynamic interactions between the hydrosphere, lithosphere, atmosphere, or biosphere.

We can define a planetary system as a celestial body in space that orbits a star and thatmaintains some level of dynamics between its lithosphere, atmosphere and hydrosphere.Some planetary systems, like the Earth, can also have a biosphere. If a planetary systemcontains a biosphere, dynamic interactions will develop between this system and thelithosphere, atmosphere and hydrosphere. These interactions can be called an environmentalsystem . Environmental systems can also exist at smaller scales of size (e.g., a single flowergrowing in a field could be an example of a small-scale environmental system).

The Earth's biosphere is made up small interacting entities called ecosystems . In anecosystem, populations of species group together into communities and interact with eachother and the abiotic environment. The smallest lining entity in an ecosystem is a singleorganism. An organism is alive and functioning because it is a biological system . Theelements of a biological system consist of cells and larger structures known as organs thatwork together to produce life. The functioning of cells in any biological system is dependenton numerous chemical reactions. Together these chemical reactions make up a chemical

system . The types of chemical interactions found in chemical systems are dependent on theatomic structure of the reacting matter. The components of atomic structure can be describedas an atomic system .

(d). Environmental Systems as Energy Systems

In the previous section we define an environmental system as a system where life interactswith the various abiotic components found in the atmosphere, hydrosphere, and lithosphere.

Environmental systems also involve the capture, movement, storage, and use of energy . Thus, environmental systems are also energy systems .

In environmental systems, energy moves from the abiotic environment to life throughprocesses like plant photosynthesis . Photosynthesis packages this energy into simple organiccompounds like glucose and starch . Both of these organic molecules can be stored for futureuse. The following chemical formula describes how plants capture the Sun's light energy andconvert it into chemical energy:

6CO 2 + 6 H 2O + light energy = C 6H 12O 6 + 6 O 2
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The energy of light is used by plants in this reaction to chemically change carbon dioxide(CO 2 ) and water ( H 2O ) into oxygen ( O 2 ) and the energy rich organic molecule glucose(C 6H 12O 6 ).

The chemical energy of photosynthesis can be passed on to other living or biotic components

of an environmental system through biomass consumption or decomposition by consumer organisms. When needed for metabolic processes, the fixed organic energy stored in anorganism can be released to do work via respiration or fermentation .

Energy also fuels a number of environmental processes that are essentially abiotic. Forexample, the movement of air by wind , the weathering of rock into soil , the formation of precipitation , and the creation of mountains by tectonic forces. The first three processesderive their energy directly or indirectly from the Sun's radiation that is received at the Earth'ssurface. Mountain building is fueled by the heat energy that exists within the Earth's interior.

Finally, the movement of energy in environmental systems always obeys specificthermodynamic laws that cannot be broken. We will learn more about these laws later inthis textbook.

(e). Food Chain as an Example of a System

A food chain models the movement of energy in an ecosystem (a form of environmentalsystem). Figure 4e-1 below illustrates the movement of energy in a typical food chain. In thisdiagram, we begin the food chain with 100,000 units of light energy from the Sun . Note, the

amount of energy available at each successive level (called trophic levels ) of this systembecomes progressively less. Only 10 units of energy are available at the last level(carnivores ) of the food chain. A number of factors limit the assimilation of energy fromone level to the next. We will examine these factors later in this textbook.
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The Sun is the original source of energy, in the

form of light, for the food chain.

(100,000 Units of Energy)

Herbivores consume approximately 10% of the plant biomass produced in a typicalfood chain.

(100 Units of Energy)

Carnivores capture and consume about 10%of the energy stored by the herbivores.

(10 Units of Energy)

Figure 4e-1 : Model of the grazing food chain showing the movementof energy through an ecosystem.

Plants capture approximately 1% of the availablelight energy from the Sun for biomass productionby way of photosynthesis. Photosynthesis can bedescribed chemically as: Light Energy + 6CO 2 +6H 2O ==> C 6H 12O 6 + 6O 2

(1,000 Units of Energy)


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Why is the above illustration an example of a system ? The concept of what makes somethinga system was fully explained in section 4b . In this topic, it was suggested that all systemsshare the following seven common characteristics:

1. Systems have a structure that is defined by its parts and processes. In the aboveexample, the structure consists of the system's three types of properties. This systemhas the following elements : the Sun, plants, herbivores and carnivores . Within thissystem the main characteristic, or attribute , of the elements being perceived is unitsof energy . The last component that makes up the structure of this system is the causeand effect relationships between the elements and attributes. For example, the Suncreates energy via nuclear fusion. This energy is radiated from the Sun's surface andreceived by the surface of the Earth. On the surface of the Earth plants capture someof this solar radiation in the chloroplasts that exist in their tissues. Throughphotosynthesis the plants convert the radiant energy into energy rich organic matter.Some of the energy fixed by the plants is passed on to herbivores throughconsumption. Finally, a portion of the energy assimilated by the herbivores is thenpassed on to carnivores through consumption.

2. Systems are generalizations of reality . The food chain process described above is asimple abstraction of what actually happens in a variety of different types of terrestrialecosystems of much greater complexity.

3. Systems tend to function in the same way. All systems consist of groups of parts thatinteract with each other according to various cause and effect processes. In the foodchain model, the parts are the Sun , plants , herbivores and carnivores . There are twomain processes taking place in this system. The first involves the movement of

energy, in the form of radiation, from the Sun to the plants. The second processinvolves the movement of energy, in the form of organic molecules, from plants toherbivores, and then finally to carnivores through biomass consumption.

4. The various parts of a system have functional as well as structural relationships between each other. The structure within the food chain is defined by the functionalrelationships between the elements and attributes of the system.

5. The fact that functional relationships exist between the parts suggests the flow and transfer of some type of energy or matter . Systems exchange energy and matterinternally and with their surrounding environment through various processes of input and output . The main material being transferred into this system (input) is energy inthe form of solar radiation . The solar radiation is then fixed into organic matter

(output) by way of photosynthesis in the plants . Herbivores consume theconstructed plant organic molecules for nutrition to run their metabolism. Theherbivores then provide food for the carnivores .

6. Systems often exchange energy and/or matter beyond their defined boundary with theoutside environment, and other systems, through various input and output processes.The organisms found in a food chains transfer organic matter into the detritus foodchain when they shed tissues or die. This transfer represnts a net output of matter outof the food chain. With decomposition, the organic matter is converted into inorganicnutrients which can be taken up by plants in the food chain to produce new organicmatter. This transfer represents a net input of matter into the food chain system.

7. Functional relationships can only occur because of the presence of a driving force .The driving force in the food chain is the Sun.
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8. The parts that make up a system show some degree of integration - in other words theparts work well together. Integration in the food chain comes primarily from theprocess of evolution. It was through evolution that plants, herbivores, and carnivorescame about and developed ecological associations between each other.

(f). Equilibrium Concepts and Feedbacks

Equilibrium

Equilibrium describes the average condition of a system, as measured through one of itselements or attributes, over a specific period of time. For the purposes of this online textbook,there are six types of equilibrium:

(1) Steady state equilibrium is an average condition of a system where the trajectory remains unchanged in time.

Figure 4f-1 : Example of the state of a steady state equilibrium over time.

(2) Thermodynamic equilibrium describes a condition in a system where the distribution of mass and energy moves towards maximum entropy .

Figure 4f-2 : Example of the state of a thermodynamic equilibrium over time.

(3) A dynamic equilibrium occurs when there are unrepeated average states through time.
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Figure 4f-3 : Example of the state of a dynamic equilibrium over time.

(4) Static equilibrium occurs where force and reaction are balanced and the properties of thesystem remain unchanged over time.

Figure 4f-4 : Example of the state of a static equilibrium over time.

(5) In a stable equilibrium the system displays tendencies to return to the same equilibriumafter disturbance .

Figure 4f-5 : Example of the state of a stable equilibrium over time.

(6) In an unstable equilibrium the system returns to a new equilibrium after disturbance .

Figure 4f-6 : Example of the state of an unstable equilibrium over time.
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Feedbacks

In order for a system to maintain a steady state or average condition the system must possessthe capacity for self-regulation . Self-regulation in many systems is controlled by negativefeedback and positive feedback mechanisms. Negative-feedback mechanisms control the

state of the system by dampening or reducing the size of the system's elements or attributes.Positive-feedback mechanisms feed or increase the size of one or more of the system'selements or attributes over time.

Interactions among living organisms, or between organisms and the abiotic environmenttypically involve both positive feedback and negative feedback responses. Feedback occurswhen an organism's system state depends not only on some original stimulus but also on theresults of its previous system state. Feedback can also involve the system state of non-livingcomponents in an ecosystem. A positive feedback causes a self-sustained change thatincreases the state of a system. Negative feedback causes the system to decease its state overtime. The presence of both negative and positive feedback mechanisms in a system results inself-regulation.

To illustrate how these mechanisms work we can hypothetically examine the changes inaphid population growth in a mid-latitude climate in the following graphical models.

Figure 4f-7 : Group of aphids feeding on the stem of a plant.

Over the winter only a few aphids survive the cold winter temperatures and scarcity of food(Figure 4f-8 ). However, warmer temperatures in the spring cause plants to start growing,providing the aphids with food. The continually increasing abundance of food increases the

fertility of individual aphids and the aphid population starts to expand exponentially. This
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situation is a positive feedback as abundant food resources cause increased reproduction andrapid population growth.

Figure 4f-8 : Increase in food abundance causes a positive effect onthe size of the aphid population. Births increase significantly and aremuch higher than deaths causing the population to expand.

By late summer the supply of plants has reached its maximum ( Figure 4f-9 ). As a result, theavailability of food to the growing aphid population becomes less per individual as timeproceeds. Less food means lower egg production and births begin to decline. When birthsreach the same level as deaths the aphid population stops growing and stabilizes. The

population is becoming too large for the food supply. The size of the population relative tofood supply produces a negative feedback as the fertility of aphids begins to decline.

Figure 4f-9 : As the abundance of food levels off aphid reproductionslows down and deaths begin to increase. Population size of theaphids begins to level off.


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With the arrival of fall cooler temperatures reduce the supply of plants causing the largeaphid population to be faced with further food scarcity ( Figure 4f-10 ). The lack of foodcauses the aphid death rate to increase and the birth rate to decrease. The population begins todecline rapidly. The reduction of food caused by the cooler temperatures enhances thenegative feedback that began in late summer.

Figure 4f-10 : The decrease in food abundance causes a negative effect on aphid populationsize. Deaths now exceed births and the population size of the aphids begins to decrease.

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Chapter 4 - Introduction to Systems Theory

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