Chapter 52

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

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 52

Population Ecology


• Population ecology is the study of populations in relation to environment, including environmental influences on density and distribution, age structure, and population size


Concept 52.1: Dynamic biological processes influence population density, dispersion, and demography

• A population is a group of individuals of a single species living in the same general area


Density and Dispersion

• Density is the number of individuals per unit area or volume

• Dispersion is the pattern of spacing among individuals within the boundaries of the population

LE 52-2

Populationsize

Emigration

Deaths

ImmigrationBirths

PopulationDynamics


• In a clumped dispersion, individuals aggregate in patches

• A clumped dispersion may be influenced by resource availability and behavior

Video: Flapping Geese (clumped)

LE 52-3a

Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.


• A uniform dispersion is one in which individuals are evenly distributed

• It may be influenced by social interactions such as territoriality

Video: Albatross Courtship (uniform)

LE 52-3b

Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.


• In a random dispersion, the position of each individual is independent of other individuals

Video: Prokaryotic Flagella (Salmonella typhimurium) (random)

LE 52-3c

Random. Dandelions grow from windblown seeds that land at random and later germinate.


Demography

• Demography is the study of the vital statistics of a population and how they change over time

• Death rates and birth rates are of particular interest to demographers


Life Tables

• A life table is an age-specific summary of the survival pattern of a population


Survivorship Curves

• A survivorship curve is a graphic way of representing the data in a life table

• The survivorship curve for Belding’s ground squirrels shows a relatively constant death rate

LE 52-4

Males

Females

10Age (years)

Num

ber o

f sur

vivo

rs (l

og s

cale

)

4 6 80 2

1,000

100

10

1


• Survivorship curves can be classified into three general types: Type I, Type II, and Type III

III

II

100Percentage of maximum life span

Num

ber o

f sur

vivo

rs (l

og s

cale

)

0 50

1,000

100

10

1

I


Reproductive Rates

• A reproductive table, or fertility schedule, is an age-specific summary of the reproductive rates in a population

• It describes reproductive patterns of a population


Per Capita Rate of Increase

• If immigration and emigration are ignored, a population’s growth rate (per capita increase) equals birth rate minus death rate

• Birth – Death = growth rate

• Zero population growth occurs when the birth rate equals the death rate


Exponential Growth

• Exponential population growth is population increase under idealized conditions

• Under these conditions, the rate of reproduction is at its maximum, called the intrinsic rate of increase


• Exponential population growth results in a J-shaped curve

Number of generations

Popu

latio

n si

ze (N

)2,000

= 1.0N

1,000

1,500

500

0151050

dNdt

= 0.5NdNdt

LE 52-10

Year

Elep

hant

pop

ulat

ion

8,000

4,000

6,000

2,000

019801960194019201900

The J-shaped curve of exponential growth characterizes some rebounding populations


Concept 52.4: The logistic growth model includes the concept of carrying capacity

• Exponential growth cannot be sustained for long in any population

• A more realistic population model limits growth by incorporating carrying capacity

• Carrying capacity (K) is the maximum population size the environment can support

LE 52-11

Population size (N)

Per c

apita

rate

of i

ncre

ase

(r)

Maximum

Positive

Negative

N = K0


• The logistic model of population growth produces a sigmoid (S-shaped) curve

Number of generations

Popu

latio

n si

ze (N

)

K = 1,5001,500

2,000

1,000

500

1510500

Logistic growth

Exponentialgrowth

= 1.0NdNdt

= 1.0NdNdt

1,500 – N1,500

LE 52-13a

Time (days)

Num

ber o

f Par

amec

ium

/mL

1,000

0

400

5

200

100

15

800

600

A Paramecium population in the lab


• Some populations overshoot K before settling down to a relatively stable density

Time (days)

Num

ber o

f Dap

hnia

/50

mL

180

0

90

20

60

400

60

150120

A Daphnia population in the lab

30

80 100 120 140 160

LE 52-13c

Time (years)

Num

ber o

f fem

ales

80

1975 1980

40

19850

1990

60

A song sparrow population in its natural habitat

20

1995 2000


The Logistic Model and Life Histories

• Life history traits favored by natural selection may vary:

• K-selection, or density-dependent selection, selects for life history traits that are sensitive to population density

• r-selection, or density-independent selection, selects for life history traits that maximize reproduction


Concept 52.5: Populations are regulated by a complex interaction of biotic and abiotic influences

• There are two general questions about regulation of population growth:

– What environmental factors stop a population from growing?

– Why do some populations show radical fluctuations in size over time, while others remain stable?


Population Change and Population Density

• In density-independent populations, birth rate and death rate do not change with population density

• In density-dependent populations, birth rates fall and death rates rise with population density

LE 52-14

Population density

Equilibriumdensity

Density-independentbirth rate

Density-dependentdeath rate

Population density

Equilibriumdensity

Density-independentdeath rate

Density-dependentbirth rate

Population density

Equilibriumdensity

Density-dependentdeath rate

Density-dependentbirth rate

per c

a pi ta

Birt

h or

dea

th ra

te

LE 52-15

10,000

Aver

age

num

ber o

f see

dspe

r rep

rodu

cing

indi

vidu

al(lo

g sc

ale)

1,000

100

100101Plants per m2 (log scale)

Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases.

Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply.

Aver

age

clut

ch s

ize

2.880

Females per unit area

3.0

3.8

4.0

3.4

3.6

3.2

60 705030 40200 10


Territoriality

• In many vertebrates and some invertebrates, territoriality may limit density


• Oceanic birds exhibit territoriality in nesting behavior


Other Factors

• Health

• Predation

• Toxic Wastes


• Many populations undergo boom-and-bust cycles

• Boom-and-bust cycles are influenced by complex interactions between biotic and abiotic factors

LE 52-21

Year

Har

e po

pula

tion

size

(thou

sand

s)

1850

Snowshoe hare

01875 1900 1925

40

80

120

160

Lynx

pop

ulat

ion

size

(thou

sand

s)

Lynx

0

3

6

9


The Global Human Population

• The human population increased relatively slowly until about 1650 and then began to grow exponentially

8000B.C.

Hum

an p

opul

atio

n (b

illio

ns)6

5

4

3

2

1

04000B.C.

3000B.C.

2000B.C.

1000B.C.

The Plague

0 1000A.D.

2000A.D.

LE 52-23

Ann

ual p

erce

nt in

crea

se

2.2

2

1.8

1.6

1.4

1.2

1

2003

2050Year

2025200019751950

0.8

0.6

0.4

0.2

0


Regional Patterns of Population Change

• To maintain population stability, a regional human population can exist in one of two configurations:

– Zero population growth = High birth rate – High death rate

– Zero population growth =Low birth rate – Low death rate

• The demographic transition is the move from the first state toward the second state

LE 52-24

Birt

h or

dea

th ra

te p

er 1

,000

peo

ple

50

40

30

20

10 Sweden

2050Year

20001900 195018500

18001750

Birth rateDeath rate

MexicoBirth rateDeath rate


Age Structure

• One important demographic factor in present and future growth trends is a country’s age structure

• Age structure is the relative number of individuals at each age

• It is commonly represented in pyramids

LE 52-25

Rapid growthAfghanistan

AgeMale

Percent of population

Female

8 6 4 2 2 4 6 80

45–4940–4435–3930–3425–2920–2415–1910–14

5–90–4

85+80–8475–7970–7465–6960–6455–5950–54

Slow growthUnited States

AgeMale


Female

6 4 2 2 4 6 80

45–4940–4435–3930–3425–2920–2415–1910–14

5–90–4

85+80–8475–7970–7465–6960–6455–5950–54

8

Decrease Italy

Male


Female

6 4 2 2 4 6 808

LE 52-26

Infa

nt m

orta

lity

(dea

ths

per 1

,000

birt

hs)

50

40

30

20

10

0Developedcountries

60

Developingcountries

Life

exp

ecta

ncy

(yea

rs)

80

40

20

0Developedcountries

60

Developingcountries


Ecological Footprint

• The ecological footprint concept summarizes the aggregate land and water area needed to sustain the people of a nation

• It is one measure of how close we are to the carrying capacity of Earth

• Countries vary greatly in footprint size and available ecological capacity

LE 52-27

Ecol

ogic

al fo

otpr

int (

ha p

er p

erso

n)14

12

10

8

6

4

16

0

2

02 4 6 8 10 12 14 16

Available ecological capacity(ha per person)

New Zealand

AustraliaCanada

Sweden

WorldChina

India

SpainUK

Japan

Germany

Norway

USA

Netherlands

Chapter 52

Documents

pearson education

benjamin cummingsin

benjamin cummingsconcept

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editionneil campbell

jane reecelectures

chris romerocopyright

random dispersion