1. Chapter 36
Population
Ecology
Lecture Outline
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2.  http://www.youtube.com/watch?v=8IKCOjE4eDM

3. 36.1 Ecology is studied
at various levels
 Ecology is the study of the interactions of organisms with
other organisms and with the physical environment
 Ecology is wide-ranging
 Habitat – the place where the organism lives
 Population – all the organisms within an area belonging to the
same species
 Community – all populations interacting at a locale (predation,
competition)
 Ecosystem – encompasses a community of populations as well
as abiotic environment (sunlight, temperature, precipitation)
 Biosphere – encompasses the zones of the Earth’s land, water,
and air where living organisms are found
36-3

4. Figure 36.1 Ecological levels
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Organism Population Community Ecosystem
Coral reef ecosystem
(Bottom): © David Hall/Photo Researchers, Inc.
36-4

5. 36.2 Population Density & Distribution
 Density
 Number of individuals per unit area
 Distribution
 Clumped, Random & Uniform
 Limiting factors effect a populations range
36-5

6. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Young, small Medium Larger
shrubs shrubs shrubs Figure 36.2A
Distribution
patterns of the
creosote bush
Clumped Random Uniform
36-6
Mature desert shrubs
(Bottom); © Richard Weymouth Brooks/Photo Researchers, Inc.

7. Figure 36.2B Nesting colony of Cape gannets off the coast of New Zealand,
uniform distribution
36-7

9. 36.3 The growth rate results in
population size changes
 A population’s annual growth rate depends on
 Number that are born & die each
 Annual immigration (coming in) & emigration (leaving)
 Biotic potential of a population is the highest
possible growth rate
 Achieved when resources are unlimited
 Rare in nature
36-9

10. 3 Types of Survivorship Curves
 Three types of survivorship curves
 Type I Survivorship: Mammals
 They survive well past the midpoint of the life span, and
death does not come until near the end of the life span
 Type II Survivorship: Hydras, songbirds, and small
mammals
 Survivorship decreases at a constant rate throughout the life
span
 Type III Survivorship: Many invertebrates and fishes
 Most individuals will probably die very young
36-10

11. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 36.3B
1,000 Three typical
survivorship
I curves
Dall sheep
Number of Survivors
100
II
hydra
10
oyster
III
0
0 50 100
Percent of Life Span
b. 36-11

12. Age Structure Diagrams

13. Exponential Growth
 Exponential Growth
 Results in j-shaped curve with 2 phases
 Lag phase – Growth is slow because the number of
individuals in the population is small
 Exponential growth phase – Growth is accelerating due to
biotic potential
 Usually, exponential growth can only continue as long
as resources in the environment are unlimited
 Ex: Human Population Growth 36-13

14. Figure 36.4A Exponential growth
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
exponential growth
phase
Number of Organisms
lag phase
Time
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15. Logistic Growth
 Logistic Growth – as resources decrease, population
growth levels off
 S-shaped curve with 4 phases
 Lag phase
 Exponential growth phase
 Deceleration phase
 Stable equilibrium phase
 Growth starts slowly, then goes through an exponential phase
 Carrying Capacity: the maximum number of organisms an
ecosystem can support.
36-15

16. Figure 36.4B Logistic growth
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
carrying capacity
Number of Organisms
stable equilibrium phase
deceleration
phase
lag exponential
phase growth
phase
Time
36-16

17. Density-independent factors
 Density-independent factors affect growth
 Percentage of individuals killed remains the same regardless
of the population size
 Abiotic (or “non-living”) factors
Exs: drought, fire, freezes, hurricanes, floods
 Example: A drought on the Galápagos Islands
 Caused the population size of finches to decline from 1,400
to 200 individuals
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18. Density-dependent factors a
 Biotic (or “living”) factors:
 Competition – when members of same species
attempt to use needed resources
 Predation – when one living organism, the predator,
eats another, the prey
36-18

19. Figure 36.5A Percentage that die per density of population
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mortality Percentage
density-independent factors
density-dependent factors
Population Density
36-19

20. Figure 36.6B Predation has a density-dependent effect. At left, when
density is low only two mice cannot find a place to hide and the hawk
cannot find them (predation rate = 0%). At right, when density is
high, 100 mice are unable to hide, and the hawk captures say ½ of
them (predation rate = 50%)
36-20

21. Opportunistic populations
 Opportunistic populations – live in a
fluctuating and/or unpredictable environments
Exs: dandelions, mice
http://www.youtube.com/watch?v=RTIlOlVT3LI
36-21

22. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 36.7A
Dandelions are
an opportunistic
species
Opportunistic Pattern
• Small individuals
• Short life span
• Fast to mature
• Many offspring
• Little or no care of offspring
© Ted Levin/Animals Animals
36-22

23. Equilibrium populations
 Equilibrium populations – live in relatively
stable and predictable environments
 Logistic population growth, and remains close to , or
at, carrying capacity
 Exs: oaks, pines, hawks, eagles, whales, elephants,
bears, gorillas
36-23

24. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 36.7B Bears are
Equilibrium Pattern
an equilibrium species
• Large individuals
• Long life span
• Slow to mature
• Few and large offspring
• Much care of offspring
© Winfried Wisniewski/Getty Images
36-24

25. Extinction
 Extinction is the total disappearance of a
species or higher group
Slow to mature, few offspring, specialists,
pretty, valuable to humans
http://www.youtube.com/watch?v=NNmTLLmhxFQ
http://www.youtube.com/watch?v=LaQd7Zfqj7g
36-25

26. 36.8 World population growth is
exponential
 World’s population has risen steadily to a
present size of about 6.8 billion people
 Doubling time: the length of time it takes for the
population size to double
 Currently, the doubling time is about 51 years
 In 51 years, the world would need double the amount of food,
jobs, water, energy, and so on just to maintain the present
standard of living
 Carrying capacity ?
36-26

27. Figure 36.8 World population growth over time
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
12
10
Population (in billions)
8
6 less-developed countries
more-developed countries
4
2
0
1750 1800 1850 1900 1950 2000 2050 2100 2150
Source: Population Reference Bureau.
36-27

28. Figure 36.8 World population growth over time (Cont.)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Living conditions in more-developed countries
Living conditions in less-developed countries
(top): © Corbis RF; (bottom): © Ben Osborne/OSF/Animals Animals
36-28

29. Connecting the Concepts: Ch. 36
 Population density & distribution
 3 types of Survivorship Curves
 Exponential vs. Logistic Growth
 Density-independent & Density-dependent Factors
 Human population growth rates worldwide
36-29