1. Chapter 52 Earth’s Fluctuating Populations
To understand human population growth we must consider the general principles of population ecology

2. Population
A group of individuals of a single species living in the same general area

3. Density and Dispersion
Density - the number of individuals per unit area or volume
Dispersion - the pattern of spacing among individuals within the boundaries of the population

4. Population Dynamics
Density is the result of a dynamic interplay between processes that add individuals to a population and those that remove individuals from it
Immigration
Births
PopuIation size
Emigration
Deaths

5. Patterns of Dispersion
Clumped dispersion
individuals aggregate in patches
may be influenced by resource availability and behavior
Uniform dispersion
individuals are evenly distributed
may be influenced by social interactions such as territoriality
Random dispersion
the position of each individual is independent of other individuals

6. Life Table
Age-specific summary of the survival pattern of a population

7. Survivorship Curve
A graphic way of representing the data in a life table
Figure 52.4
1000
100 10 1
Number of survivors (log scale) 2 4 6 8
Age (years)
Males
Females

8. Semelparity “Big-bang” reproduction Reproduce a single time and die
Figure 52.6

9. Iteroparity Repeated reproduction
Produce offspring repeatedly over time

10. “Trade-offs” and Life Histories
Two types of reproductive strategies
Many offspring with little energy put into each one.
i.e. a plant that releases many small seeds
Few offspring with more energy put into each one.
i.e. a plant that releases less large seeds with a store of energy to help the seed surive and germinate

11. Exponential Growth
The exponential model describes population growth in an idealized, unlimited environment

12. Exponential population growth results in a J-shaped curve
Exponential growth is characteristic of some populations that are rebounding
Figure 52.10
1900
1920
1940
1960
1980
Year
2,000
4,000
6,000
8,000
Elephant population

13. The Logistic Growth Model
In the logistic population growth model the growth rate declines as carrying capacity is reached
Carrying capacity (K) is the maximum population size the environment can support
800
600
400
200
Time (days) 5 10 15
1,000
Number of Paramecium/ml
The logistic model of population growth produces a sigmoid (S-shaped) curve

14. Population Change and Population Density
Density-independent
Birth rate and death rate do not change with population density
Density-dependent
Birth rates fall and death rates rise with population density

15. Limiting Factors-factors that affect the carrying capacity
Density-independent factors
Weather (storms, cold, drought)
Some diseases (DDT poisoning)
Density-dependent factors
Food or Predators
Space or Shelter
Other diseases (rabies)

16. Population Cycles Many populations
Undergo regular boom-and-bust cycles
Figure 52.21
Year
1850
1875
1900
1925 40 80
120
160 3 6 9
Lynx population size (thousands)
Hare population size (thousands)
Lynx
Snowshoe hare
Boom-and-bust cycles are influenced by complex interactions between biotic and abiotic factors

17. The Global Human Population
The human population increased relatively slowly until about 1650 and then began to grow exponentially
Figure 52.22
8000 B.C.
4000 B.C.
3000 B.C.
2000 B.C.
1000 B.C.
1000 A.D.
The Plague
Human population (billions)
2000 A.D. 1 2 3 4 5 6

18. Though the global population is still growing
The rate of growth began to slow approximately 40 years ago
Figure 52.23
1950
1975
2000
2025
2050
Year
2003
Percent increase
2.2 2
1.6
1.4
1.2 1
0.8
0.6
0.4
0.2
1.8

19. 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

20. Population structure
A population that is 75% adults, 25% juveniles is very different from a population of 25% adults and 75% juveniles.

21. Population structure
Age structure – distribution of ages in a population.
Size structure – distribution of sizes in a population.

22. Age structure is commonly represented in pyramids
Figure 52.25
Rapid growth Afghanistan
Slow growth United States
Decrease Italy
Male
Female
Age 8 6 4 2
Percent of population
80–84
85
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
20–24
25–29
10–14
5–9
0–4
15–19

23. Infant mortality and life expectancy at birth vary widely among developed and developing countries but do not capture the wide range of the human condition
Figure 52.26
Developed countries
Developing countries
Infant mortality (deaths per 1,000 births)
Life expectancy (years) 60 50 40 30 20 10 80

24. Ecological footprints for 13 countries
Show that the countries vary greatly in their footprint size and their available ecological capacity
Figure 52.27 16 14 12 10 8 6 4 2
New Zealand
Australia
Canada
Sweden
World
China
India
Available ecological capacity (ha per person)
Spain UK
Japan
Germany
Netherlands
Norway
USA
Ecological footprint (ha per person)

25. At more than 6 billion people
The world is already in ecological deficit
No population can exponentially grow forever
No exceptions!