Guide 32
Population Ecology - Human Population Growth
http://www.toothpastefordinner.com/archives/2004/Apr/
Demography
• Demography is the study of the vital statistics of
a population
– And how they change over time
• Death rates and birth rates
– Are of particular interest to demographers
• A life table
Life Tables
– Is an age-specific summary of the survival pattern of
a population
– Is best constructed by following the fate of a cohort
Sand Flys and Leishmania
• The life table of Belding’s ground squirrels
– Reveals many things about this population
• The survivorship curve for Belding’s ground squirrels
– Shows that the death rate is relatively constant
Number of survivors (log scale)
1000
100
Females
10
Males
1
0
2
4
6
Age (years)
8
10
• Survivorship curves can be classified into three general
types
– Type I, Type II, and Type III
Number of survivors (log scale)
1,000
I
100
II
10
III
1
0
50
Percentage of maximum life span
100
https://ibess.wikispaces.com/Human+Survivorship+-+by+KunYang
The Global Human Population
• The human population
– Increased relatively slowly until about 1650 and
then began to grow exponentially
5
4
3
2
The Plague
1
8000
B.C.
4000
B.C.
3000
B.C.
2000
B.C.
1000
B.C.
0
1000
A.D.
0
2000
A.D.
Human population (billions)
6
• Human population growth has slowed after
centuries of exponential increase
• No population can grow indefinitely
– And humans are no exception
World human
population in millions, in
10-year intervals, since
1950.
Populations of Humans are not evenly Distributed
http://navdeep-humanpopulation.blogspot.com/2007/12/we-all-know-that-human-population-has.html
Like all animal populations, there is a defined
carrying capacity for the human population.
http://www.algebralab.org/practice/practice.aspx?file=Reading_CarryingCapacity.xml
Actual population size is a function of both Fertility rates and
Death rates. These are influenced by available technology.
http://www.globalchange.umich.edu/globalchange2/current/lectures/human_pop/human_pop.html
http://www.globalchange.umich.edu/globalchange2/current/lectures/human_pop/human_pop.html
Humans by Era
Upper Paleolithic
Neolithic
Bronze Age and Iron Age
Classical Greece
Classical Rome
Pre-Columbian North America
Medieval Islamic Caliphate
Medieval Britain
Early Modern Britain
Early 20th Century
Current world average
http://en.wikipedia.org/wiki/Life_expectancy
Average Lifespan at Birth
(years)
33
20
35+
28
28
25-30
35+
30
40+
30-45
67.2
Death Rates
Age Structure
• One important demographic factor in present
and future growth trends
– Is a country’s age structure, the relative number of
individuals at each age
• Age structure
– Is commonly represented in pyramids
Rapid growth
Afghanistan
Male
Female
8 6 4 2 0 2 4 6 8
Percent of population
Figure 52.25
Age
85
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
Slow growth
United States
Female
Male
8 6 4 2 0 2 4 6 8
Percent of population
Age
85
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
Decrease
Italy
Female
Male
8 6 4 2 0 2 4 6 8
Percent of population
Regional Patterns of Population Change
• To maintain population stability
– A regional human population can exist in one of two
configurations
– Zero population growth = High birth rates – High
death rates
– Zero population growth = Low birth rates – Low
death rates
• The demographic transition
– Is the move from the first toward the second state
Birth or death rate per 1,000 people
50
40
30
20
10
Sweden
Mexico
Birth rate
Birth rate
Death rate
Death rate
0
1750
Figure 52.24
1800
1850
1900
Year
1950
2000
2050
The End