Chapter 36Population

EcologyLecture Outline

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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

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f S

urv

ivo

rs

b.

50 100Percent of Life Span

III

oyster

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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

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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

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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

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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

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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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