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Hunters and gatherers
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Forecasting population growth
Low population density
Early, pre-industrial agriculture
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Allowed a much greater density of people
The first major increase in human population
Machine age
3.
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Industrial revolution increased possibility of increased density
Significant increase in EROI
The Modern era
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Rate of population has slowed in wealthy nations but continues
to increase rapidly in poorer, less developed nations.
Throstur Thorsteinsson
[email protected]
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Four stages
1.
2.
3.
4.
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3 and 4 occurred at the
same time
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Taking what nature gives you - hardly any
domination
Omnivorous non-specialist animal
Competed with other species in food-webs
Constrained by available
photosynthetic energy
Low life expectancy,
low population density
12000 BP in southwestern Asia
8000 – 9000 BP in China and Mexico
Involved:
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Hunters gatherers
Pre-industrial
agriculture
Industrial agriculture
Industrial revolution
Domestication of plants and animals
Initially shifting cultivations (slash and
burn) - sustainable?
Increased population
density from 2 to 25 – 1000
persons per km2.
Throstur Thorsteinsson ([email protected])
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UAU102F
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Fall
Why did they “go for it”?
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Saw the prospects for a better life?
Needed to in order to survive - possible that
the population had increased beyond what the
H&G systems could sustain
Gave more reliable food supplies
Provided higher energy return
Enabled higher population
densities
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Cultural Implications of the transition:
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What were the Cultural Implications?
What were the Environmental Implications?
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Environmental Implications:
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Less time devoted to gathering food
Cultural evolution
Increased population density
Beginning of Urbanization
Social stratification
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Large areas of forest cleared
Increased population density and thus land
could not lay fallow as needed
Soil erosion
Distribution of plants and animals shifted in
favor of domesticates
Diseases - monocultures made the system
vulnerable
The ancient city of Mohenjo-daro, built around
2600 BC by the Ancient Indus valley civilization
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Slowly progressing domination
Development of irrigation and fertilization
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Simple machines such as simple plows and irrigation
systems
Land did not need to lay fallow
Population density continued to increase
EROI remained relatively low
(energy return on investment)
Throstur Thorsteinsson ([email protected])
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Energy return on investment (EROI)
Describes how much energy is invested in
the system compared to what we get out.
Energy out/energy in
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Can be used as an indicator of scarcity
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Began in China ca 1200 with the use of coal
Slowly progressed as various inventions
enabled more efficient use of energy
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Increased use of inputs
Increased use of outputs and waste
Increased pressure on the environment
Thomas Malthus 1798 (classical economist)
“Essay on the Principle of Population”
Populations increase in size exponentially
Food supplies increase linearly
Thus population growth will outstrip the food
resources, with catastrophic consequences—mass
starvation, poverty, and economic and social collapse.
True? Why/why not?
140
Linear
Exponential
120
100
Value
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Humans became energy slaves!
Possible to link major changes in human
history to changes in energy use.
Enabled increased population densities
Urbanization and urban growth
New human enterprises
Increased production in less time:
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Steam engine (coal)
Internal combustion engine (oil)
Gas turbines
80
60
40
20
0
4
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Time
Throstur Thorsteinsson ([email protected])
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UAU102F
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Ester Boserup 1965:
“The conditions of Agricultural Growth”
Population growth triggers higher
productivity through land intensification
and innovation of new technology improving the human condition.
Julian Simon: More people, more minds
Formula to represent population change:
Pt = Pt-1 + (B – D) + (I – E)
P: population at time (t) or at time (t-1)
B: Births
D: Deaths
I: Immigration
E: Emigration
Some Statistics see: http://www.census.gov/ipc/www/idb/
 Current Population: 7,342,192,000 (28 September 2016)
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Human population grows exponentially
Economic growth (goods and services produced),
increase as well – and due to the laws of
thermodynamics this growth requires material
and energy inputs.
Pressures on resources and the environment
mount - BUT how can we know what the impact
on the environment may be if population keeps
growing at current rates?
Crude birth rates: average annual births/1000 population
Crude death rates: average annual deaths/1000 population
Total fertility rate: average number of children a woman has from
15-49 yrs old
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Rate of natural increase: birth rate-death rate
Net growth rates: birth rate-death rate
Infant mortality rates: Annual number of death of infants under the age
of 1 per 1000 life births
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Life expectancy at birth: Average number of years a newborn
infant can expect to live under current mortality levels
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Age-specific death and birth rates: Age class effects taken into
account
Throstur Thorsteinsson ([email protected])
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the expected number of children born per woman in her child-bearing years
CIA World Factbook of 2015
The World FactBook (CIA) - https://www.cia.gov/library/publications/the-worldfactbook/fields/2127.html, CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=7248239
http://vizhub.healthdata.org/le/
Throstur Thorsteinsson ([email protected])
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http://world.bymap.org/MedianAge.html
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Current Population (1 Jan 2015): ~329 100
Crude Births per 1000 indiv:
13.9
Crude Deaths per 1000 indiv:
6.3
Annual growth rate:
1.2%
Infant Mortality per 1000 indiv: 2.1
Life Expectancy (at birth):
83
Total Fertility Rate:
2.0 per woman
https://hagstofa.is/media/49889/hag_160621b.pdf
Doubling time
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Current Population(2008):
18,931,686
Crude Births per 1000 indiv:
42
Crude Deaths per 1000 indiv:
12
Annual growth rate:
3.0 %
Infant Mortality per 1000 indiv:
75.3
Life Expectancy (at birth):
55.1
Total Fertility Rate:
5.86 per woman
dN
 r N r: growth rate
dt
N  N0 exp( r  t )
Doubling time
N  2 N0  N0 exp( r  t2 x )
Take natural log at both sides…
t2 x 
ln( 2) 0.7

r
r
or 70/(growth rate in %)
More data, Population Reference Bureau
http://www.prb.org/DataFinder
Throstur Thorsteinsson ([email protected])
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UAU102F
Fall
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Population age structure:
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The proportion of the population in each age
class – also called age cohorts
Affects current and future birth rates, death
rates and growth rates
Has an impact on the environment
Has complications for current and future social
and economic status.
So-called age class effects!
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What do these show in terms of growth?
Important for resource management e.g. deer
Demographic transition:
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Three-stage pattern of change in birth rates and death rates.
Occurred during the process of industrial and economic
development of Western nations.
Leads to a decline in population growth.
Stage I: High birth and death rates - death rate declining Undeveloped
Stage II: High growth rate (high birth rate, lower death rate) transition
Stage III: Birth rate drops toward the death rate, leading to
low or zero growth rate.
Stage IV: same as stage II, but now due to disease….
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Cause specific death rate: number of deaths
from one cause per 100,000 total deaths
Incidence rate: Number of people
contracting a disease per 100 people per
timeperiod
Prevalence rate: Number of people afflicted
by a disease at a particular time
Morbidity: Occurrence of disease in a
population
Throstur Thorsteinsson ([email protected])
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How can we do this? - three models
Mathematical extrapolation
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Linear Growth
Exponential
Logistic growth
Cohort Component Method
(most common for humans)
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Systems Models
(more complex, used at e.g. IIASA)
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UAU102F
Fall
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Exponential growth
Characterizes
anything that can
grow without limit
Same as
compounding
formula in economics
Pt+N = Pt*(1+r)^N
Pt+1 = Pt*(1+r) ^1
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Logistic or density
dependent growth
Upper limit to the
ultimate size - carrying
capacity, K
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Constant
Can be assessed
Growth determined by:
Pt = P t-1 + r* Pt-1 * (K - Pt-1)/K
Definition:
The maximum population of a species an
area can support without reducing its
ability to support the same species in the
future
Function both of the area and the organism
(ex. Ceteris paribus (= all other things being equal or held constant)
Larger area higher K)
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Determined by size limiting factors, such as
space, food, energy etc.
Affects birth and death rates.
What determines K – and can it be
estimated?
B
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Human carrying capacity
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Factors:
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Food supply
Land and soil resources
Water resources
NPP
Population density
Technology
Is it static?
Biophysical carrying capacity
Social carrying capacity
Throstur Thorsteinsson ([email protected])
T1
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Breaks population into
age cohorts (usually 5
year) by gender, ethnicity
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Cohort specific death and
birth rates.
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Cohort specific
immigration/emigration
T2
B
D
0-4
0-4
5-9
5-9
10-14
10-14
15-19
15-19
D
D
D
D
D
D
D
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UAU102F
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Where are these pyramids from ?
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Population expected
to reach 10 billions in
2050
GDP/capita to
increase 2 - 4 fold
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If P really is a culprit for environmental
degradation - how can it be reduced?
Should we?
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Ethics?
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Throstur Thorsteinsson ([email protected])
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