This document outlines key concepts in population ecology, including: 1) Ecology is studied at various levels from organisms to populations, communities, ecosystems, and the biosphere. 2) Population density and distribution can be clumped, random, or uniform and are affected by limiting factors. 3) Population growth rates depend on births, deaths, immigration and emigration and can follow exponential or logistic growth curves depending on available resources.

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

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

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

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

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. 36-14
Figure 36.4A Exponential growth
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
lag phase
NumberofOrganisms
exponential growth
phase
Time

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

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
36-17

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

20. 36-20
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%)

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

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

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

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

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