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IV. SYSTEM

What is a system? – very important in modelling

Term “system” is used very often => definition?

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2. SYSTEM

Many deffinitions:"Any phenomenon, either structural or functional, having at least two

separable components and some interaction between these components may be considered a system."

Hall, Day

"The whole is more than the sum of parts."Bertalanffy

= common to the most definitions: ” a system is a combination of parts that interact and produce some new quality in their interaction”

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2. SYSTEM

Example:Two atoms of hydrogen combine with one atom of oxygen to

produce a molecule of water.The properties of a water molecule are entirely different than

those of hydrogen or oxygen, which are elements that water is constructed from.

Water molecule is a system that is made of 3 elements: two hydrogen atoms and one oxygen atom.

The elements interact. This interaction binds the elements together and results in new quality displayed by the whole

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2. SYSTEM: Elements – whole

System can be seen as a: - whole - combination of elements

An element is a building block of a system : => it has its own properties, features

Case “Cake”:Pieces of cake are not components of the cake =>

there are no differences between them, they may differ in size only => a piece of a whole is not an element.

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2. SYSTEM: part – whole

Case “cake”:If you separate the crust, the filling and the topping in your

cake, you will get something quite different from the whole cake.

It will make much more sense to call these parts the elements of the whole.

The taste of different elements will be different, there are ways to separate one element from another.

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2. SYSTEM: part – whole

Group of the elements don't necessarily present the system.

Case: ChessGroup of 32 chess figures: they look different and

they have specific properties => we can not call them a system

We add two elements: chessboard and rules of interaction => we got a system = chess

=> New quality has emerged, which is different from any quality of particular parts which consist chess.

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2. SYSTEM: Reductionism – holism

Holism: system’s point of view=> focus is on interactions between the elements at the system level => study of the behavior at the system level and not at the level of system’s elements

Reductionism: understanding of system’s behavior based on=> studies of characteristics of particular elements which consist the system => studies of the interactions between these elements

"The features of the complex, compared to those of the elements, appear as "new" or "emergent""

Bertalanffy

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2. SYSTEM: Reductionism – holism

Both approaches are applicable and useful.

Reductionistic approach: - decompose complex system on sub systems which are less complex - doesn't enable to understand behavior of the whole system

Holistic approach:- enables understanding of functioning/behavior of the system at the system level- if the properties of subsystems (elements) are known then it is much easier to obtain knowledge about the system properties

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Reductionist vs. holist causality

Reductionism: Seek explanation at lower level in the hierarchy– Build understanding of whole by detailed study of parts

+2 4 + 3 + 2+ 1=

Holism: Not everything can be explained by lower levels– “The whole is greater than the sum of its parts”

+2 4 + 3 + 2+ 1>

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2. SYSTEM: Reductionism – holism

(A) A list of the elements that consist the system desnt’t enable description of the system.

(B) Elements can be linked together on different ways. Descriptions of this links are needed.

(C) Qualitative description of the interactions: => direction of the interactions – orientation(arrows) of connections between the elements => element can be liked by itself as well (it behavior depends on itself) => Does have x element positive or negative influence on the element y?

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2. SYSTEM: Reductionism – holism

There may be two types of relationships between elements: - Flows of matter/energy/money (water, food, cement, heat,

light, electricity, $, €)

- Flows of information: element B has transferred information to element C abut the element A (weight, volume, height, …) while the element A was not affected with this information transfer at all.

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2. SYSTEM: Reductionism – holism

Case “breakfast”:=> when we are eating there is a flow from the plate to our mouth => when we look at the clock and we consider that we need to hurry to the job, the flow of information was established from the clock to us (no flow on matter)

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2. SYSTEM: Reductionism – holism

The flows may have different functions: - stimulation of the receptor (positive feedback)- reduction of the activity of the receptor (negative

feedback)

- Positive feedback – process is going out of control- Negative feedback – leveling the system at the

steady-state point

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1. Time: – How long? How often? When?– How does it Change over time?

2. Space: – How big? How deep, What shape?– What arrangement?– How does it Change over space ?

3. Ecological complexity:– What ‘levels of organization’?– Trophic complexity?– Physical complexity?– Change with complexity

SYSTEM: ecological scale (3-Dimensions)

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Extrapolation of information from one time, space or complexity scale to another.

?

? ?

?

?

?

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Regional

GlobalLocal

René Dubos: “Think globally act locally”Systems Ecology: Think and relate info across multiple scales

Cross-scale effects

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2. SYSTEM: structure - function

Structure of the system is defined by the elements which consist it and the interactions between them.

Complexity of the structure increasing with the number of the elements and with the interactions between them.

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Structure vs. Function (≈Pattern vs. Process)Structure: physical characteristics

– Biotic and abiotic factors– Abundance and arrangement in space

Function: relationships, flows and processes– Flow of energy, cycling of matter, control mechanisms

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2. SYSTEM : hierarchy

Supersystem – system – subsystem"In any hierarchical structure the higher levels embrace or

"compre-hend" the lower, but the lower are unable to comprehend the higher. This is what may be called the"hierarchical principle""

Each system can be a part of larger system or can be split in to smaller sub systems.

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2. SYSTEM : hierarchy

Hierarchy: decomposition of the system on sub systems, which can be still decomposed further down => hierarchical levels

Systems at the same hierarchical level has similar complexity and function, but there are significant differences in complexity and functions between levels

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2. SYSTEM: hierarchy

When we study the properties of particular system, we need to define its hierarchical position(level):

=> the system is under the influences of the system at the higher hierarchical level, and also under the influences of the systems at the samehierarchical level.

=> The influence of lower levels are very low (may be neglected)

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Graded series of compartments arranged according to scale

Hierarchy

Energy

Money

Material Information

Lewis Center

Compostable solids

Recyclables

WastewaterGas release

Material Output

Glass

Metals Plastics

Cellulose

Recyclables

Office

Glossy Cardboard

Newspaper

Cellulose fiber

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Hierarchy of disciplines

– Biospherics– Environmental science– Systems ecology– Ecosystems ecology– Community ecology– Population biology– Organism biology– Histology– Cellular biology– Molecular biology– Molecular genetics– Chemistry– Subatomic physics

A scaling hierarchy of natural science

Increasing scales of time and

space Causality from

theR

eductionist perspective

Hierarchy of matter– Universe– Galaxies– Solar system– Planets– Earth– Biosphere– Biomes– Ecosystems– Communities– Populations– Organisms– Organ systems– Tissues– Cells– Organelles– Molecules– Atoms– Subatomic particles

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Systems perspective of hierarchical level

Phenomena must be understood in the context of the systems in which they occur ( nested in hierarchical structure)

Need to study whole systems as integrated units

f(parts + feedback)=

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Feedback interaction

The returning of part of the output of a system to be reintroduced as input– (+) feedback reinforces change– (-) feedback counteracts change

f(parts + feedback)=

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Properties of systems with feedbackEmergent properties:

– Properties that are only manifest in a whole systems contextAutonomy:

– Behavior of system is partially independent of outside influenceScale dependence:

– Feedback effects only apparent above scale of individual components

f(parts + feedback)=

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Feedback control mechanisms

Cybernetic system:– “A special class of cause-and-effect (input-output) systems in which

input is determined, at least in part, by output.” (Patten and Odum 1981)

Types of feedback control– Teleological systems: feedback is centralized in control structures– Determinate systems: feedback is diffuse and self-organizing

Input OutputCybernetic

System

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Feedback at different levels of organizationMechanism differ with system type and scale

Space

Tim

e

Stimulus Response

Environment

Nutrients

Centralized (teleological) control

Decentralized (determinate) control

Decentralized (determinate) control

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Feedback types: Negative feedbackChange leads to (counteracted):

– Stabilization– Self-regulation – “Goal-seeking”– Homeostatic

e.g. temperature regulation in organisms and machines

Bodytemperature

Sweat ( + )

( - )

( - )

Roomtemperature

Airconditioner

( + )

( - )

( - )

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Feedback types: Positive

Change leads to further change in same direction– Growth enhancing– Potentially destablizing

( + )

( + )

( + )

Population size

Population growth

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Examples of negative feedback

Hunger

FoodConsumption

( + )

( - )

( - )

Bodytemperature

Sweat( + )

( - )

( - )

Foxpopulation

Hare population

( + )

( - )

( - )

Badbehavior

Punishment( + )

( - )

( - ) ?

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Examples of positive feedback

Bankbalance

Interestadded/month

( + )

( + )

( + )

Health conditions

Natural resources(“natural capital”)

Poverty anddesperation( - )

( - )

( + )

( + )

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Examples of coupled feedback:

In a finite world, positive feedback is ultimately always constrained by the 2nd law of energy and by

material resources

( + )

( + )

( + )

Starvationinfertilitydisease

( - )

( - )

( + )

Human population

( + )

( + )

( + )

Births

Health conditions

Natural resources(“natural capital”)

Poverty anddesperation( - )

( - )

( + )

( + )

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1) Introduced Species

Prevalence of fire Prompting grasses

Fire frequency& intensity

Land clearingdisturbance

( +)

( - )

( + )( + )

( + )

Prevalence of Native species

( - )

( -)( + )

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2) Global desertification

Spatial heterogeneity of Soil resourcesGrazing

( +)

( + )( + )

Prevalence of Desert shrubs

( + )( +)

Erosion &Gas emissions

Barren areaBetween shrubs

( +) ( +)( + )

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3) Missing C sinks and sources

Temperature

PrimaryProductivity

Mineralization ofSoil organic mater

(SOM)

( + )

( +)

( +)Nitrogen available

For plant uptake

( + )

AtmosphericCO2 ( -)

( - )

( + )

( +)( +) ( + )

Temperature

AtmosphericCO2

Terrestrialrespiration

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37Space Tim

e

4) RegulationRegulation via feedback is present at all levelsSpecific control mechanism and patterns differ with system type and scale

Stimulus Response

Environment

Nutrients

Centralized control

Decentralized control

Decentralized control

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5) Integration with larger systemMechanism and patterns differ with system type and scale

Space Tim

e ←Causality

→

Energy

Matter

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2. SYSTEM: Exercise 1

1. List the names of three systems. How would you describe them?

2. Describe the system “chicken soup with noodles”! What are the elements? What is the function of the system? What dose it make system from the soup elements?

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2. SYSTEM: Exercise 2

1. List five parts for each of the following four systems:

- Washing machine:- Oak tree:- Croissant :- City:

2. Which system consists from the following parts:water, pebbles, three fishes, fish food, water plants? What happen if we add diver? Can elements (parts of the system) give complete description of the system?

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2. SYSTEM : Exercise 3

1. Place the forest tree into hierarchical structure. List two lower and two higher hierarchical levels.

2. Is it possible that the system is under the influence of the system which is three levels higher but not from the systems from first and second higher level. Is such a case possible at all?

3. Do sub system survive if the “zero” system fall apart. List some cases!