Chapter 36 Population Ecology Lecture Outline Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 36Population
EcologyLecture Outline
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
http://www.youtube.com/watch?v=8IKCOjE4eDM
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
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Figure 36.1 Ecological levels
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Organism
Coral reef ecosystem
Population Community Ecosystem
(Bottom): © David Hall/Photo Researchers, Inc.
36.2 Population Density & Distribution
Density Number of individuals per unit area
Distribution Clumped, Random & Uniform Limiting factors effect a populations range
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Figure 36.2A Distribution
patterns of the creosote bush
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Clumped Random Uniform
Mature desert shrubs
Largershrubs
Mediumshrubs
Young, smallshrubs
(Bottom); © Richard Weymouth Brooks/Photo Researchers, Inc.
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Figure 36.2B Nesting colony of Cape gannets off the coast of New Zealand, uniform distribution
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
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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
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Figure 36.3B Three typical survivorship
curves
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1,000
100
10
00
Nu
mb
er o
f S
urv
ivo
rs
b.
50 100Percent of Life Span
III
oyster
IIhydra
IDall sheep
Age Structure Diagrams
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
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Figure 36.4A Exponential growth
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lag phase
Nu
mb
er o
f O
rgan
ism
s
exponential growthphase
Time
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.
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Figure 36.4B Logistic growth
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.N
um
ber
of
Org
anis
ms
stable equilibrium phase
carrying capacity
decelerationphase
exponentialgrowthphase
lagphase
Time
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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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
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Figure 36.5A Percentage that die per density of populationCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mo
rta
lity
Pe
rcen
tag
e
density-independent factorsdensity-dependent factors
Population Density
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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 ishigh, 100 mice are unable to hide, and the hawk captures say ½ of
them (predation rate = 50%)
Opportunistic populations
Opportunistic populations – live in a fluctuating and/or unpredictable environments
Exs: dandelions, mice
http://www.youtube.com/watch?v=RTIlOlVT3LI
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Figure 36.7A Dandelions are an opportunistic
species
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© Ted Levin/Animals Animals
• Small individuals
• Short life span
• Fast to mature
• Many offspring
• Little or no care of offspring
Opportunistic Pattern
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
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Figure 36.7B Bears are an equilibrium species
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© Winfried Wisniewski/Getty Images
• Large individuals
• Long life span
• Slow to mature
• Few and large offspring
• Much care of offspring
Equilibrium Pattern
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
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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
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Figure 36.8 World population growth over time
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
less-developed countriesmore-developed countries
Po
pu
lati
on
(in
bil
lio
ns)
Source: Population Reference Bureau.
1750 1800 1850 1900 1950 2000 2050 2100 2150
0
2
4
6
8
10
12
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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.
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
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