Chapter 36

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

PowerPoint Lectures forBiology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon

Lectures by Chris Romero

Chapter 36Chapter 36

Population Dynamics


The Spread of Shakespeare’s Starlings

• The European Starling

– Has become an abundant and destructive pest in North America

Europeanstarling


• Starling populations have become very successful

– And spread throughout North America since their introduction in 1890

Current

1955

1945

1935 1925

19151905

19251935

1945

1955Current

The spread of starlings across North America


• Population ecology

– Is concerned with changes in population size and the factors that regulate populations over time


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


POPULATION STRUCTURE AND DYNAMICS

36. 2 Density and dispersion patterns are important population variables

• Population density

– Is the number of individuals of a species per unit of area or volume


• Environmental and social factors

– Influence the spacing of individuals in various dispersion patterns: clumped, uniform, or random

Figure 36.2A Figure 36.2B


36.3 Life tables track mortality and survivorship in populations

• Life tables and survivorship curves

– Predict an individual’s statistical chance of dying or surviving during each interval of the individual’s lifetime

Table 36.3


• The three types of survivorship curves

– Reflect species’ differences in reproduction and mortality

Pe

rce

nta

ge

of

surv

ivo

rs (

log

sca

le) 100

10

1

0.10 50 100

III

II

I

Percentage of maximum life spanFigure 36.3


36.4 Idealized models help us understand population growth


The Exponential Growth Model

• Exponential growth

– Is the accelerating increase that occurs when growth is unlimited


• The equation G rN describes this J-shaped curve

– G the population growth rate

– r an organism’s inherent capacity to reproduce

– N the population size

Figure 36.4A

Time Number of Cells

0 minutes

20

40

60

80

100

120 (= 2 hours)

3 hours

4 hours

8 hours

12 hours

1

2

4

8

16

32

64

512

4,096

16,777,216

68,719,476,736

= 20

= 21

= 22

= 23

= 24

= 25

= 26

= 29

= 212

= 224

= 236

Num

ber

of b

acte

rial c

ells

(N

)

70

60

50

30

40

20

10

00 20 40 60 80 100 120 140

G = r N

Time (min)


Limiting Factors and the Logistic Growth Model

• Limiting factors

– Are environmental factors that restrict population growth

Bre

edin

g m

ale

fur

seal

s(t

hous

ands

)10

8

6

4

2

01915 1925 1935 1945

YearFigure 36.4B


• Logistic growth

– Is the model that represents the slowing of population growth as a result of limiting factors

– Levels off at the carrying capacity, which is the number of individuals the environment can support

Nu

mb

er

of

ind

ivid

ua

ls (

N)

K

0Time

G = r N

G = r N(K – N)

K

Figure 36.4C


• The equation G rN(K – N)/K describes a logistic growth curve

– Where K carrying capacity and (K – N)/K accounts for the leveling off of the curve


36.5 Multiple factors may limit population growth

• As a population’s density increases

– Factors such as limited food supply and increased disease or predation may increase the death rate, decrease the birth rate, or both

4.0

3.6

3.8

3.4

3.2

3.0

2.80 10 20 30 40 50 60 70 80

Density of females

Clu

tch

size

Figure 36.5A


• Abiotic factors such as weather

– May limit many natural populations

Exponentialgrowth

Suddendecline

Num

ber

of

aph

ids

Apr May Jun Jul Aug Sep Oct Nov DecFigure 36.5B


• Most populations

– Are probably regulated by a mixture of factors, and fluctuations in numbers are common

Time (years)

1975 1980 1985 1990 1995 20000

20

40

80

60

Num

ber

of f

emal

es

Figure 36.5C


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

• Some populations

– Undergo regular boom-and-bust cycles of growth and decline

160

120

80

40

01850 1875 1900 1925

9

6

3

0

Snowshoe hare

Lynx

Har

e po

pula

tion

size

(tho

usan

ds)

Lynx

pop

ulat

ion

size

(tho

usan

ds)

Year Figure 36.6


36.7 Evolution shapes life histories

• An organism’s life history

– Is the series of events from birth through reproduction to death

LIFE HISTORIES AND THEIR EVOLUTION


• Populations with so-called r-selection life history traits

– Produce many offspring and grow rapidly in unpredictable environments

Figure 36.7A


• Populations with K-selected traits

– Raise few offspring and maintain relatively stable populations


• Life history traits

– Are shaped by natural selection

Experimentaltransplant ofguppies

Predator: Killifish;preys mainly on small,immature guppies

Guppies: Larger atsexual maturity thanthose in pike-cichlidpools

Predator: Pike-cichlid;preys mainly on large,mature guppies

Guppies: Smaller atsexual maturity thanthose in killifish poolsFigure 36.7B


36.8 Principles of population ecology have practical applications

• Principles of population ecology

– Are useful in managing natural resources

CONNECTION

900

800

700

600

500

400

300

200

100

01960 1970 1980 1990 2000

Yie

ld (

thou

sand

s of

met

ric t

ons)

Figure 36.8


THE HUMAN POPULATION CONNECTION

The Plague

6

5

4

3

2

1

08000B.C.

4000B.C.

3000B.C.

2000B.C.

1000B.C.

0 1000A.D.

2000A.D.

Hum

an p

opul

atio

n si

ze (

billi

ons)

Figure 36.9A

36.9 Human population growth has started to slow after centuries of exponential increase

•The human population

– Has been growing almost exponentially for centuries, standing now at about 6.4 billion


• The ecological footprint

– Represents the amount of land per person needed to support a nation’s resource needs

16

14

12

10

8

6

4

2

00 2 4 6 8 10 12 14 16

Available ecological capacity (ha per person)

Eco

log

ica

l fo

otp

rint

(ha

pe

r p

ers

on

)

Japan

UK

Spain

Germany

NetherlandsNorway

USA

World

ChinaIndia

Sweden

Canada

Australia

New Zealand

Figure 36.9B


• The ecological capacity of the world

– May already be smaller than the population’s ecological footprint

Traffic in downtown Cairo, Egypt

Manhattan,New York City

Refugee camp in ZaireFigure 36.9C


36.10 Birth and death rates and age structure affect population growth

• The demographic transition

– Is the shift from high birth rates and death rates to low birth rates and death rates

50

40

30

20

10

01900 1925 1950 1975 2000 2025 2050

Year

Birth rate

Death rate

Birt

h or

dea

th r

ate

per

1,00

0 po

pula

tion

Figure 36.10A


• The age structure of a population

– Is the proportion of individuals in different age-groups

– Affects its future growth

Age85+

80–8475–7970–7465–6960–6455–5950–5445–4940–4435–3930–3425–2920–2415–1910–145–90–4

8 46 2 0 2 4 6 8 6 4 2 0 2 4 6 6 4 2 0 2 4 6

Percent of population Percent of population Percent of population

Primaryreproductive

ages

Rapid growth Slow growth Decrease

Afghanistan United States Italy

Male Female Male Female Male Female

Figure 36.10B


• Increasing the status of women

– May help to reduce family size

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Chapter 36