biology sylvia s. mader michael windelspecht chapter 44 population ecology lecture outline copyright...

BiologySylvia S. Mader

Michael Windelspecht

Chapter 44 Population

EcologyLecture Outline

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Outline• 44.1 Scope of Ecology• 44.2 Demographics of Populations• 44.3 Population Growth Models• 44.4 Regulation of Population Size• 44.5 Life History Patterns• 44.6 Human Population Growth

44.1 Scope of Ecology

• Ecology The study of the interactions of organisms with

• Other organisms and the physical environment Habitat - Place where an organism lives Population - All the individuals of a species within a

particular space Community – Various populations of multiple species

interacting with each other Ecosystem - Community interacting with the

environment Biosphere - All the communities on Earth whose

members exist in air and water and on land3

Ecological Levels

4

Organism Population Community Ecosystem

© David Hall/Photo Researchers, Inc.


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44.2 Demographics of Populations

• Demography is the statistical study of a population

• Demography includes Population density Population distribution Growth rate of a population

Demographics of Populations

• Density and Distribution Population Density - Number of individuals

per unit area Population Distribution - Pattern of

dispersal of individuals across an area of interest

Limiting factors are environmental aspects that particularly determine where an organism lives

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Distribution Patterns of the Creosote Bush

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Young, smallshrubs

b. Clumped

Largeshrubs

a. Mature desert shrubs

Mediumshrubs

c. Random

d. Uniform

(a): © The McGraw Hill Companies, Inc. Evelyn Jo Johnson, photographer


• Population Growth The rate of natural increase depends on

• The number of individuals born each year, and• The number of individuals who die each year

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• Population Growth (continued) Biotic Potential

• The maximum rate of natural increase for a population that can occur when resources are unlimited

Biotic potential depends on factors that influence the population’s reproduction, including

• The usual number of offspring surviving to reproductive age

• The amount of competition within the population• Age of and number of reproductive opportunities• Presence of disease and predators

Biotic Potential

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a. b.(mice): © E. R. Degginger/Photo Researchers, Inc.; (rhinos): © Corbis RF


• Mortality Patterns A cohort

• Composed of all the members of a population born at the same time

– Life tables demonstrate how many members of a cohort are still alive after certain intervals of time

Survivorship• The probability that newborn individuals of a cohort

will survive to a particular age

• Survivorship Curves– A plot of the number of organisms surviving at each age

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A Life Table for a Bluegrass Cohort

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• Survivorship Curves Type I

• Characteristic of a population in which most individuals survive past the midpoint of the life span and death does not come until the end of the life span

Type II• Death is linear over time (unrelated to age)

Type III• Typical of a population in which most individuals die very

young

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Survivorship Curves

14b: © Holt Studios/Photo Researchers, Inc.; c: © Bruce M. Johnson; d: © Digital Vison/Getty RF Images

I

I

II

III

III

Nu

mb

er o

f S

urv

ivo

rs

Percent of Life Span

Nu

mb

er o

f S

urv

ivo

rs


b. Bluegrasses

d. Mosquitoes

1,000

100

10

00 50 100

1 million

10,000

100

0

0 50 100

50

Death occurs after midpoint.

Death unrelated to age.

Death comes early on.

II

Nu

mb

er o

f S

urv

ivo

rs


a.

c. Lizards


Nu

mb

er o

f S

urv

ivo

rs

1,000

100

10

0

0 50 100

1,000

100

10

00 100



• Age Distribution The proportion of the population that falls into various

age categories There are three major age groups

• Prereproductive• Reproductive• Postreprodutive

At least three age structure diagrams are possible• Increasing population• Stable population• Decreasing population

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Age Structure Diagrams

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Increasing Population Decreasing PopulationStable Population

Age Structure

Postreproductive Ages

Reproductive Ages

Prereproductive Ages


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44.3 Population Growth Models

• Two working models for population growth: Semelparity

• Members of a population have only a single reproductive event in their lifetime

– Ex: insects

Iteroparity• Members of the population experience many

reproductive events throughout their lifetime– Ex: most vertebrates, shrubs, and trees

Patterns of Reproduction

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a. b.


a: © Breck P. Kent/Animals Animals/Earth Scenes; b: © Doug Sokell/Visuals Unlimited

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Population Growth Models

• Exponential Growth Rate of population growth increases as the total

number of females increases Biotic potential is having full effect and birthrate is

a maximum during exponential growth Phases of an exponential growth curve

• During the lag phase, growth is small because the population is small.

• During the exponential growth phase, growth is accelerating.

Model for Exponential Growth

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1 2 3 4 5 6 7 8 90

Generation PopulationSize

Number ofFemales

10.0

24.0

57.6

138.2

331.7

796.1

1,910.6

4,585.4

11,005.0

26,412.0

63,388.8

12

28.8

69.1

165.9

398.1

955.3

2292.7

5502.5

13206.1

31694.5

a.

70

60

50

40

30

20

10

10

R = 2.4

exponential growth

lag

b.

c.

Generations

Po

pu

lati

on

(th

ou

san

ds)

To calculate population size from year to year, use this formula:

Nt+1 = RNt

Nt = number of females already present

R = net reproductive rate

Nt+1 = population size the following year

5

10

9

8

7

6

5

3

4

2

1

0


• Logistic growth Occurs when limiting environmental factors

oppose growth Phases of a logistic growth curve

• During the lag phase, growth is slow because the population is small.

• During the exponential growth phase, growth is accelerating.

• During the deceleration phase, growth slows down.• During the stable equilibrium phase, there is little if

any growth.

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Model for Logistic Growth

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100

200

300

400

700

600

500

2 4 6 8 10 12 14 16 18

a.

b.

c.

0

2

4

6

8

1012

14

16

18

9.6

29.0

71.1

174.6

350.7

513.3594.4

640.8

655.9

661.8

0

19.4

42.1

103.5

176.1

162.681.1

46.4

15.1

5.9

Nt

K

lag

deceleration

Nt

Growth of Yeast Cells in Laboratory Culture

Time (t )(hours)

Number ofindividuals (N)

Number of individualsadded per 2-hour period

Nu

mb

er

of

Yea

st C

ells

exponentialgrowth

stableequilibriumphase

Time (hours)

To calculate population growth as time passes, use thisformula:

N = population size

N/t = change in population size

r = rate of natural increase

K = carrying capacity

K – N = effect of carrying capacity on population growth

= rNK

K – N



• Carrying Capacity The maximum number of individuals of a

species the environment can continuously support

• The closer the population to the carrying capacity, the more likely its resources will become scarce and that biotic effects such as competition and predation will become apparent

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44.4 Regulation of Population Size

• Density-independent Factors The population density does not influence

the intensity of the factor’s effect• Natural disasters

• Density-dependent Factors The percentage of the population affected

increases as the population density increases• Competition• Predation• Parasitism

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Density-independent Effects

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a. Low density of mice b. High density of mice


Density-dependent Effect

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2,000

1,500

1,000

500

01910 1920 1930 1940 1950

Nu

mb

er o

f R

ein

dee

r

exponentialgrowth

decline asa resultof suddenresourcedepletion


© Paul Janosi/Valan Photos

Density-dependent Effects -- Competition

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a. Low density of birds b. High density of birds

Density-dependent Effects -- Predation

28a. Low density of mice b. High density of mice


44.5 Life History Patterns

• Life histories contain characteristics of a population such as The number of births per reproduction The age of reproduction The life span The probability of an individual living the entire life span

• Each population distributes energy among its life span, reproduction events, and care of offspring.

• Related species may have different life history patterns.

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Parental Care Among Frogs and Toads

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a. Mouth-brooding frog,Rhinoderma darwinii

b. Strawberry poison arrow frog,Dendrobates pumilio

c. Midwife toad, Alyces obstetricans

(a): © Michael Fogden/Animals Animals; (b): © Michael Fogden/Animals Animals;(c): © Tom McHugh/Photo Researchers, Inc.


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Life History Patterns

• r is the rate of natural increase of a population.

• K is the carrying capacity of the environment.

• Some populations are subject to r-selection, and other populations are subject to K-selection.

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• r - Selection In unstable or predictable environments, population

growth is controlled by density-independent factors. Population size is low relative to K.

• r - Strategists (opportunistic species) Produce large numbers of offspring Have a small body size Mature early Have a short life span Do not invest energy in parental care Tend to be good dispersers and colonizers


• K - Selection In stable, predictable environments, population size is

controlled by density-dependent factors. Population size tends to be near K.

• K - Strategists (equilibrium species) Produce small numbers of offspring Have a large body size Mature late Have a long life span Invest energy in parental care Tend to be strong competitors

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Life History Strategies

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(dandelions): © Ted Levin/Animals Animals; (bears): ©Michio Hoshino/Minden Pictures

Opportunistic Species(r-strategist)

• Small individuals• Short life span

• Fast to mature• Many offspring• Little or no care of offspring

• Many offspring die before reproducing

• Early reproductive age

Equilibrium Species(K-strategist)

• Large individuals• Long life span

• Slow to mature• Few and large offspring• Much care of offspring

• Most young survive to reproductive age

• Adapted to stable environment

Ecology Focus: When a Population Grows Too Large

• White-tailed deer are prolific breeders

Female deer breed their first year, and once they start breeding, produce about two young each year of life.

• A century ago, the white-tailed deer population was less than half a million

• Today, it is well over 200 million

• Natural predators of deer, such as wolves and mountain lions, are now absent from most regions.

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Ecology Focus: When a Population Grows Too Large

• Populations that are too large may suffer from starvation as they deplete their own food supply

• For example, after deer hunting was banned on Long Island, New York, the deer population quickly outgrew available food resources

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44.6 Human Population Growth

• The human population is undergoing exponential growth Present size is 6.7 billion people

• The doubling time of the human population is currently estimated at 52 years

• Population Size 1800 1 Billion 1930 2 Billion 1960 3 Billion 2012 6 Billion

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Human Population Growth

• More-Developed Countries (MDCs) North America, Europe, Japan, and Australia

Slow population growth

High standard of living

A demographic transition (decreased death rate followed by decreased birth rate) has occurred, so population growth has stabilized.

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• Less-Developed Countries (LDCs) Latin America, Africa, and Asia Rapid population growth Low standard of living Strategies to reduce population growth

• Family planning programs

• Social progress, which may reduce the desire for large families

• Delay the onset of childbearing

World Population Growth

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lowest growth

highest growth

less-developed countries

more-developed countries

a. b.

Bil

lio

ns

of

Peo

ple

1750

2

4

6

8

10

12

01800 1850 1900 1950 2008 2250

Year


b(Top): © The McGraw-Hill Companies, Inc./Jill Braaten, photographer; b(Bottom): © Robert Harding/Robert Harding World Imagery/Corbis


• Age Distributions Populations of MDCs and LDCs can be

divided into three age groups• Prereproductive• Reproductive• Postreproductive

MDCs and LDCs have different age structure diagrams

• Many MDCs have a stable age structure• Most LDCs have a youthful profile and are

experiencing population growth42

Age Structure Diagrams

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80+75–79

70–7465–6960–64

55–5950–54

45–4940–44

35–39

30–3425–29

20–2415–1910–14

5–9

0–4

80+75–79

70–74

65–6960–64

55–59

50–5445–49

40–4435–3930–34

25–29

20–2415–19

10–14

5–9

0–4

0

b. Less-developed countries (LDCs)

c.

a. More-developed countries (MDCs)

Millions

Millions

postreproductive

reproductive

prereproductive

300 300250 250200 200150 150100 10050 50

Ag

e (i

n y

ears

)A

ge

(in

yea

rs)

postreproductive

reproductive


c: © Still Pictures/Peter Arnold, Inc.


• Population Growth and Environmental Impact Environmental impact of a population is

measured in terms of:• Population size• Resource consumption per capita • Resultant pollution due to resource consumption

There are two types of overpopulation• Overpopulation due to population growth• Overpopulation due to increased resource

consumption 44

Environmental Impact Caused byMDCs & LDCs

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Population Hazardous Waste Production Consumption

a. b.

c.

paper

metals

fossil fuels

MDCs = more-developed countries LDCs = less-developed countries

MDCs22%

LDCs10%

LDCs40%

MDCs60%

LDCs25%

MDCs75%

MDCs80%

LDCs20%

MDCs90%

LDCs78%

biology sylvia s. mader michael windelspecht chapter 44 population ecology lecture outline copyright...

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