Lecture 1.2: Population and feedback systems



Understanding SYSTEMS!
•A set of inter-relationships between components or parts that function together to act as a whole
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•A system is simultaneously both a system and a part of a larger system
Digestive system
Economic system
Computer system

Hierarchy
•A system is simultaneously both a system and a part of a larger system
•Something that is both a part and a whole has been called a “holon”, the basic part—wholes of a
hierarchy

Systems Theory - boundaries
System
(Self,
Campus,
City,
State,
Nation)
Environment

Defining energy systems
•Isolated systems no exchange with surrounding
•Unrealistic, for comparison only
•Closed systems exchange energy, not matter
•Earth can be thought of as a closed system
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•Open systems exchange energy and matter
•All environmental systems are open systems

OPEN SYSTEMS are characterized by the continual input, throughflow, and output of matter and energy
– ALL ENVIRONMENTAL SYSTEMS ARE OPEN SYSTEMS


H
Input Environment
Output Environment
New perspective, system is focus of two environments
System
Environment
Old perspective, dichotomy between system and environment

A system is an assemblage of parts that function in some way as a whole
•Establish a system boundary
•What are the parts inside the system?
•How are they connected?
•Receives inputs
•Generates outputs
•When outputs become inputs that is feedback –
•posses capacity for self-organization (growth) and self-regulation (stability)
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Thermodynamic systems-
•Energy is the ability to do work
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•Forms of energy: potential, kinetic, thermal, chemical, electrical, etc.
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•1st Law of Thermodynamics:
• energy cannot be created or destroyed
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•2nd Law of Thermodynamics:
• energy goes from a high quality to a lower
• quality during each energy transformation; while energy is conserved, its ability to due work
decreases
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What is life?
•Biological systems build structure (they grow) and maintain (metabolize) complex structures within
their boundaries by diverting high-quality energy and exporting low-quality.
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•“The device by which an organism maintains itself at a fairly high level of orderliness consists
in continually sucking orderliness from its environment” –Schrödinger. 1944. What is life? p.73.

FEEDBACK as a consequence of interconnections
Ecological Systems possess capacity for
(a) self-regulation: negative feedback - deviation damping, stabilizing
(b) self-adaptation: positive feedback - deviation-amplifying, destabilizing
http://www.gerrymarten.com/human-ecology/images/02-8-english.gif

10.7: Homeostasis and Feedback - Biology LibreTexts
Stabilizes body temperature





Positive feedback – when the signal is amplified and moves the system further from its original
condition
Sound system
Biological growth is a positive feedback
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Input-Output models – Box and arrow models
X
Storage
amount
Flow
Amount/time
X
Water in bathtub
(liters)
Faucet
Liters/second
Drain
Liters/second
X
Students at MU
Matriculation
Students/year
Graduation
Students/year
X
World population
(people)
Births
People/year
Deaths
People/year
Input
Output
Transfer
Job
X
Students at MU
Matriculation
Students/year
Graduation
Students/year
Leave university
Students/year

Input Output models
X
Storage
amount
Flow
Amount/time
X
U.S. Population
Births
People/year
Deaths
People/year
X
World population
(people)
Births
People/year
Deaths
People/year
Immigration
People/year
Emigration
People/year

Input Output relations
X
Storage
amount
Input>output
Input=output
Input<output
Flow
Amount/time
Storage increases
Storage decreases
Storage remains same level

Input Output relations
X
Storage
amount
Input>output
Flow
Amount/time
X
U.S. Population
335,000,000 people
4,130,550
People/year
2,797,250
People/year
1,015,050
People/year
Change in population = Births + Net migration – deaths
4,130,550 people/year +1,015,050 people/year – 2,797,250 people/year = 2,348,350 people/year
New population at time t = initial population + change in population * years (t)
335,000,000 people + 2,348,350 people/year * 1 year = 337,348,350 people
Deaths
Births
Net migration

Input Output relations
U.S. Oil reserves (2020)
43.8 billion barrels
X
Storage
Units of some amount
Input<output
Flow
Amount/time units
0
barrels/day
9.5
Million barrels/day

Input Output relations
Bank Account
$3000
X
Storage
Units of some amount
Input=output
Flow
Amount/time units
Income
$1,000/ mo
Expenses
$1,000/ mo
When input = output, this is called steady state system
The system is changing but balanced

Practice making some input-output models of systems of your choice
•Can you quantify the flows and compare input and output?


Exponential growth



Exponential growth



Exponential growth



Exponential growth



Exponential growth



Exponential growth – unbound growth in the context of resource constraints
Jar is half-full at 11:59


Exponential growth



Exponential growth



Exponential Growth quotes
•The greatest shortcoming of the human race is our inability to understand the exponential
function.
•Albert A. Bartlett
•Our principal constraints are cultural. During the last two centuries we have known nothing but
exponential growth and in parallel we have evolved what amounts to an exponential-growth culture, a
culture so heavily dependent upon the continuance of exponential growth for its stability that it
is incapable of reckoning with problems of non-growth.
•M. King Hubbert
•Anyone who believes exponential growth can go on forever in a finite world is either a madman or
an economist.
•Kenneth E. Boulding

Things to think about
•Habits of a systems thinker


https://waterscenterst.org/systems-thinking-tools-and-strategies/habits-of-a-systems-thinker/