Chapter 36 Introduction Population Ecology · 85.7 92.3 36.8 CONNECTION: Principles of population ecology have practical applications Sustainable resource management involves –

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© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

PowerPoint Lectures for

Campbell Biology: Concepts & Connections, Seventh EditionReece, Taylor, Simon, and Dickey

Chapter 36 Population EcologyIntroduction

Individual emperor penguins face the rigors of the Antarctic climate and have special adaptations, including a

– downy underlayer of feathers for insulation and

– thick layer of fat for energy storage and insulation.

The entire population of emperor penguins reflects group characteristics, including the

– survivorship of chicks and

– growth rate of the population.

© 2012 Pearson Education, Inc.

Population ecologists study natural population

– structure and

– dynamics.

Introduction


Figure 36.0_1

Chapter 36: Big Ideas

Population Structureand Dynamics

The Human Population

1985

Male Female

Figure 36.0_2

POPULATION STRUCTURE AND DYNAMICS


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36.1 Population ecology is the study of how and why populations change

A population is a group of individuals of a single species that occupy the same general area.

Individuals in a population

– rely on the same resources,

– are influenced by the same environmental factors, and

– are likely to interact and breed with one another.


A population can be described by the number and distribution of individuals.

Population dynamics, the interactions between biotic and abiotic factors, cause variations in population sizes.



Population ecology is concerned with

– the changes in population size and

– factors that regulate populations over time.

Populations

– increase through birth and immigration to an area and

– decrease through death and emigration out of an area.



36.2 Density and dispersion patterns are important population variables

Population density is the number of individuals of a species per unit area or volume.

Examples of population density include the

– number of oak trees per square kilometer in a forest or

– number of earthworms per cubic meter in forest soil.

Ecologists use a variety of sampling techniques to estimate population densities.


Within a population’s geographic range, local densities may vary greatly.

The dispersion pattern of a population refers to the way individuals are spaced within their area.


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Dispersion patterns can be clumped, uniform, or random.

– In a clumped pattern

– resources are often unequally distributed and

– individuals are grouped in patches.



Figure 36.2A

Figure 36.2A_1

In a uniform pattern, individuals are

– most likely interacting and

– equally spaced in the environment.



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Figure 36.2B Figure 36.2B_1

In a random pattern of dispersion, the individuals in a population are spaced in an unpredictable way.



Figure 36.2C

Figure 36.2C_1

36.3 Life tables track survivorship in populations

Life tables track survivorship, the chance of an individual in a given population surviving to various ages.

Survivorship curves plot survivorship as the proportion of individuals from an initial population that are alive at each age.

There are three main types of survivorship curves.

– Type I

– Type II

– Type III


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Table 36.3 Figure 36.3

Percentage of maximum life span50 1000

0.1

1

10

100

III

II

I

Per

cen

tag

e o

f su

rviv

ors

(lo

g s

cale

)

36.4 Idealized models predict patterns of population growth

The rate of population increase under ideal conditions is called exponential growth. It can be calculated using the exponential growth model equation, G = rN, in which

– G is the growth rate of the population,

– N is the population size, and

– r is the per capita rate of increase (the average contribution of each individual to population growth).

Eventually, one or more limiting factors will restrict population growth.


Figure 36.4A

Time (months)

Po

pu

lati

on

siz

e (N

)

0 1 2 3 4 5 6 7 8 9 1011 120

50

100

150

200

250

300

350

400

450

500

Figure 36.4A_1

Time (months)

Po

pu

lati

on

siz

e (N

)

01 2 3 4 5 6 7 8 9 10 11 12

50

100

150

200

250

300

350

400

450

500

Figure 36.4A_2

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Table 36.4A

The logistic growth model is a description of idealized population growth that is slowed by limiting factors as the population size increases.

To model logistic growth, the formula for exponential growth, rN, is multiplied by an expression that describes the effect of limiting factors on an increasing population size.

K stands for carrying capacity, the maximum population size a particular environment can sustain.

36.4 Idealized models predict patterns of population growth

This image cannot currently be displayed.


G = rN(K N)

K

Figure 36.4B

Year1915 1925 1935 1945

0

2

4

6

8

10

Bre

edin

g m

ale

fur

seal

s(t

ho

usa

nd

s)

Figure 36.4B_1

Year1915 1925 1935 1945

0

2

4

6

8

10

Bre

ed

ing

mal

e fu

r se

als

(th

ou

san

ds)

Figure 36.4B_2 Figure 36.4C

G rN

K

0Time

Nu

mb

er o

f in

div

idu

als

(N)

G rN (K N)K

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Table 36.4B

36.5 Multiple factors may limit population growth

The logistic growth model predicts that population growth will slow and eventually stop as population density increases.

At increasing population densities, density-dependent rates result in

– declining births and

– increases in deaths.


Figure 36.5A

Number of breeding pairs

Ave

rag

e cl

utc

h s

ize

0 10 20 30 40 50 60 70 80 90

8

9

10

11

12 Intraspecific competition is

– competition between individuals of the same species for limited resources and

– is a density-dependent factor that limits growth in natural populations.



Limiting factors may include

– food,

– nutrients,

– retreats for safety, or

– nesting sites.



Figure 36.5B

Density (beetles/0.5 g flour)

Su

rviv

ors

(%

)

0 20

20

40

60

80

100

40 60 80 100 120

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In many natural populations, abiotic factors such as weather may affect population size well before density-dependent factors become important.

Density-independent factors are unrelated to population density. These may include

– fires,

– storms,

– habitat destruction by human activity, or

– seasonal changes in weather (for example, in aphids).



Figure 36.5C

Month

Exponentialgrowth

Suddendecline

Apr May Jun Jul Aug Sep Oct Nov Dec

Nu

mb

er o

f ap

hid

s

36.6 Some populations have “boom-and-bust” cycles

Some populations fluctuate in density with regularity.

Boom-and-bust cycles may be due to

– food shortages or

– predator-prey interactions.


Figure 36.6

Snowshoe hare

Lynx

Year1850 1875 1900 1925

0

3

6

9

Lyn

x p

op

ula

tio

n s

ize

(th

ou

san

ds)

0

40

80

120

160

Har

e p

op

ula

tio

n s

ize

(th

ou

san

ds)

Figure 36.6_1

Lyn

x p

op

ula

tio

n s

ize

(th

ou

sa

nd

s)

Har

e p

op

ula

tio

n s

ize

(th

ou

sa

nd

s)

Snowshoe hare

Lynx

Year1925190018751850

0

40

80

120

160

0

3

6

9

Figure 36.6_2

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36.7 EVOLUTION CONNECTION: Evolution shapes life histories

The traits that affect an organism’s schedule of reproduction and death make up its life history.

Key life history traits include

– age of first reproduction,

– frequency of reproduction,

– number of offspring, and

– amount of parental care.



Populations with so-called r-selected life history traits

– produce more offspring and

– grow rapidly in unpredictable environments.

Populations with K-selected traits

– raise fewer offspring and

– maintain relatively stable populations.

Most species fall between these two extremes.



A long-term project in Trinidad

– studied guppy populations,

– provided direct evidence that life history traits can be shaped by natural selection, and

– demonstrated that questions about evolution can be tested by field experiments.


Figure 36.7

Pool 1Predator: Killifish;preys onsmallguppies

Guppies:Larger atsexual maturity

Pool 2Predator: Pike-

cichlid;preys on large guppies

Guppies: Smaller atsexual maturity

Hypothesis: Predator feeding preferences caused difference in life historytraits of guppy populations.

Pool 3Pools with killifishbut no guppiesprior to transplant

Results

Experiment:Transplantguppies

Males Females

Males Females

Control:Guppies from pools withpike-cichlids as predators

Experimental:Guppies transplanted to poolswith killifish as predators

92.3

185.6161.5

85.7

76.1

58.248.5

67.5

200160120

8040

4020

6080

100

Ag

e o

f g

up

pie

sat

mat

uri

ty (

day

s)M

ass

of

gu

pp

ies

at m

atu

rity

(m

g)

Figure 36.7_s1



Figure 36.7_s2






Hypothesis: Predator feeding preferences caused difference in lifehistory traits of guppy populations.

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Figure 36.7_s3






Hypothesis: Predator feeding preferences caused difference in lifehistory traits of guppy populations.

Pool 3Pools with killifishbut no guppiesprior to transplant

Experiment:Transplantguppies

Figure 36.7_2

Control:Guppies from pools withpike-cichlids as predators

Experimental:Guppies transplanted to poolswith killifish as predators

Males Females Males Females

67.5 76.1

161.5185.6

4080

120160200 100

80604020

Ag

e o

f g

up

pie

sat

mat

uri

ty (

day

s)

Mas

s o

f g

up

pie

sat

mat

uri

ty (

mg

)

48.558.2

85.7 92.3

36.8 CONNECTION: Principles of population ecology have practical applications

Sustainable resource management involves

– harvesting crops and

– eliminating damage to the resource.

The cod fishery off Newfoundland

– was overfished,

– collapsed in 1992, and

– still has not recovered.

Resource managers use population ecology to determine sustainable yields.


Figure 36.8

1960 1970 1980 1990 20000

100

200

300

400

500

600

700

800

900

Yie

ld (

tho

usa

nd

s o

f m

etri

c to

ns)

THE HUMAN POPULATION


36.9 The human population continues to increase, but the growth rate is slowing

The human population

– grew rapidly during the 20th century and

– currently stands at about 7 billion.


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Figure 36.9A

Population increase

Total population size

Year1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 2000 2050

0

2

4

6

8

10

Tota

l p

op

ula

tio

n (

in b

illio

ns)

An

nu

al i

ncr

ease

(in

mil

lio

ns)

20

40

60

80

100


The demographic transition

– is the shift from high birth and death rates

– to low birth and death rates, and

– has lowered the rate of growth in developed countries.


Figure 36.9B

1900 1925 1950 1975 2000 2025 2050Year

Rate ofincrease

Birth rateDeath rate

0

10

20

30

40

50

Bir

th o

r d

eath

rat

ep

er 1

,000

po

pu

lati

on In the developing nations

– death rates have dropped,

– birth rates are still high, and

– these populations are growing rapidly.



Table 36.9

The age structure of a population

– is the proportion of individuals in different age groups and

– affects the future growth of the population.



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Population momentum is the continued growth that occurs

– despite reduced fertility and

– as a result of girls in the 0–14 age group of a previously expanding population reaching their childbearing years.



Figure 36.9C

Male Female Male Female Male Female

1985 2010 20358075–7970–7465–6960–6455–5950–5445–4940–4435–3930–3425–2920–2415–1910–14

5–90–4

Ag

e

6 5 4 3 2 1 0 1 2 3 4 5 6 45 3 2 1 0 1 2 3 4 5 1 0 1 2 3 4 545 3 2Population in millions

Total population size 76,767,225Estimated population in millions

Total population size 112,468,855Projected population in millions

Total population size 139,457,070

Figure 36.9C_1

Male Female

1985

0–4

Ag

e

6Population in millions


5–910–1415–1920–2425–2930–3435–3940–4445–4950–5455–5960–6465–6970–7475–79

80

5 4 3 2 1 0 1 2 3 4 5 6

Figure 36.9C_2

0–4

Ag

e

5–910–1415–1920–2425–2930–3435–3940–4445–4950–5455–5960–6465–6970–7475–79

80

5 4 3 2 1 0 1 2 3 4 5

Male Female

2010

Estimated population in millionsTotal population size 112,468,855

Figure 36.9C_3

0–4

Ag

e

5–910–1415–1920–2425–2930–3435–3940–4445–4950–5455–5960–6465–6970–7475–79

80

5 4 3 2 1 0 1 2 3 4 5

Male Female

2035

Projected population in millionsTotal population size 139,457,070

36.10 CONNECTION: Age structures reveal social and economic trends

Age-structure diagrams reveal

– a population’s growth trends and

– social conditions.


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Figure 36.10

Birth years

80–8475–7970–7465–6960–6455–5950–5445–4940–4435–3930–3425–2920–2415–1910–14

5–90–4

Ag

e

85Male Female

1985

before 19011901–19051906–10

1911–151916–20

1921–251926–301931–351936–40

1941–451946–50

1951–551956–601961–65

1971–751976–80

1981–85

1966–70

12 10 8 6 4 2 0 2 4 6 8 10 12Population in millions


Birth years Male Female2010


12 10 8 6 4 2 0 2 4 6 8 10 12Estimated population in millions

Total population size 310,232,863Projected population in millions


12 10 8 6 4 2 0 2 4 6 8 10 12

before 19261926–30

1931–351936–40

1941–451946–50

1951–551956–60

1961–651966–701971–751976–801981–85

1986–901991–95

1996–20002001–20052006–2010 2031–35

2026–302021–252016–202011–152006–102001–05

1996–20001991–951986–90

1981–851976–801971–751966–701961–65

1956–601951–55

before 1951

Figure 36.10_1

Birth years

0–4

Ag

e

Male Female

1981–85

Population in millionsTotal population size 238,466,283

1985

5–910–1415–1920–2425–2930–3435–3940–4445–4950–5455–5960–6465–6970–7475–7980–84

85

1976–801971–75

1966–701961–651956–601951–55

1946–501941–45

1936–401931–351926–301921–251916–201911–15

1906–101901–1905

before 1901

12 10 8 6 4 2 0 2 4 6 8 10 12

Figure 36.10_2


0–4

Ag

e

5–910–1415–1920–2425–2930–3435–3940–4445–4950–5455–5960–6465–6970–7475–7980–84

85

Estimated population in millionsTotal population size 310,232,863

12 10 8 6 4 2 0 2 4 6 8 10 12

2006–20102001–20051996–20001991–951986–90

1981–851976–801971–75

1966–701961–65

1956–60

1946–501951–55

1941–451936–401931–35

1926–30before 1926

Figure 36.10_3

Birth years Female2035

0–4

Ag

e

5–910–1415–1920–2425–2930–3435–3940–4445–4950–5455–5960–6465–6970–7475–7980–84

85

12 10 8 6 4 2 0 2 4 6 8 10 12

Male

2031–35

Projected population in millionsTotal population size 389,531,156

2026–302021–252016–202011–152006–102001–05

1996–20001991–951986–90

1981–851976–801971–751966–70

1961–651956–60

1951–55before 1951

36.11 CONNECTION: An ecological footprint is a measure of resource consumption

The U.S. Census Bureau projects a global population of

– 8 billion people within the next 20 years and

– 9.5 billion by mid-21st century.

Do we have sufficient resources to sustain 8 or 9 billion people?

To accommodate all the people expected to live on our planet by 2025, the world will have to double food production.


An ecological footprint is an estimate of the amount of land required to provide the raw materials an individual or a nation consumes, including

– food,

– fuel,

– water,

– housing, and

– waste disposal.



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The United States

– has a very large ecological footprint, much greater than its own land, and

– is running on a large ecological deficit.

Some researchers estimate that

– if everyone on Earth had the same standard of living as people living in the United States,

– we would need the resources of 4.5 planet Earths.



Figure 36.11A

Figure 36.11A_1 Figure 36.11A_2

Figure 36.11B

Ecological Footprints(gha per capita)

0–1.51.5–3.03.0–4.54.5–6.06.0–7.57.5–9.09.0–10.5 10.5Insufficient data

You should now be able to

1. Define a population and population ecology.

2. Define population density and describe different types of dispersion patterns.

3. Explain how life tables are used to track mortality and survivorship in populations.

4. Compare Type I, Type II, and Type III survivorship curves.

5. Describe and compare the exponential and logistic population growth models, illustrating both with examples.


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6. Explain the concept of carrying capacity.

7. Describe the factors that regulate growth in natural populations.

8. Define boom-and-bust cycles, explain why they occur, and provide examples.

9. Explain how life history traits vary with environmental conditions and with population density.

10. Compare r-selection and K-selection and indicate examples of each.



11. Describe the major challenges inherent in managing populations.

12. Explain how the structure of the world’s human population has changed and continues to change.

13. Explain how the age structure of a population can be used to predict changes in population size and social conditions.

14. Explain the concept of an ecological footprint. Describe the uneven use of natural resources in the world.


Figure 36.UN01

Percentage of maximum life spanPer

cen

tag

e o

f su

rviv

ors

Few large offspring,low mortalityuntil old age

Many smalloffspring,high mortality

I

II

III

Figure 36.UN02

Male Female

1985

Population in millionsTotal populationsize 76,767,225

Population in millionsTotal population

size 112,468,855

6 5 4 3 2 1 0 1 2 3 4 5 6 5 4 3 2 1 0 1 2 3 4 5

Ag

e

8075–7970–7465–6960–6455–5950–5445–4940–4435–3930–3425–2920–2415–1910–14

5–90–4

Male Female

2010

Figure 36.UN03

G rNK

(K N)

Figure 36.UN04

Time

Bir

th o

r d

eat

h r

ate

I II III IV

16

Figure 36.UN05

Documents

Chapter 36 Introduction Population Ecology · 85.7 92.3 36.8 CONNECTION: Principles of population ecology have practical applications Sustainable resource management involves –