Chapter 36

Copyright © 2009 Pearson Education, Inc.

PowerPoint Lectures forBiology: Concepts & Connections, Sixth EditionCampbell, Reece, Taylor, Simon, and Dickey

Chapter 36Chapter 36 Population Ecology

Lecture by Brian R. Shmaefsky


Introduction: A Tale of Two Fishes

Population ecology is concerned with

– Changes in population size

– Factors that regulate populations over time

It helps explain the biodiversity of an environment


Ecologists learn the structure and dynamics of natural populations

With this information they are better equipped to

– Develop sustainable food sources

– Assess the impact of human activities

– Balance human needs with the conservation of biodiversity and resources

Introduction: A Tale of Two Fishes


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

Population

– 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

– Are likely to interact and breed with one another


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

Population dynamics is the interactions between

– Biotic and abiotic factors

It is the cause of variation in population sizes

– A population increases through birth and immigration

– Death and emigration out of an area decrease the population

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


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

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

– The 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


Video: Flapping Geese (clumped)

Video: Albatross Courtship (uniform)

Video: Prokaryotic Flagella (Salmonella typhimurium) (random)


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

Dispersion patterns can be

– Clumped

– Uniform

– Random



In a clumped pattern individuals are grouped in patches



In a uniform pattern individuals are equally spaced in the environment



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



36. 3 Life tables track survivorship in populations

Life tables track survivorship over the life span of individuals in a population

Survivorship curves plot the proportion of individuals alive at each age

– Type I

– Type II

– Type III

Percentage of maximum life span

Per

cen

tag

e o

f su

rviv

ors

(lo

g s

cale

)

0 50 1000.1

1

10

100

III

II

I


36.4 Idealized models predict patterns of population growth

Exponential growth model

– The rate of population increases under ideal conditions

– Calculated using the equation G = rN

– G is the growth rate of the population

– N is the population size

– r is the per capita rate of increase

Time (months)

Po

pu

lati

on

siz

e (N

)

0 1 2 3 4 5 6 7 8 9 10 11 120

50

100

150

200

250

300

350

400

450

500


Logistic growth model

– This growth model takes into account limiting factors

– Limiting factors are environmental factors that restrict population growth

– Formula


(K N)G = rN

K

Year

Bre

edin

g m

ale

fur

seal

s(t

ho

usa

nd

s)

1915 1925 1935 19450

2

4

6

8

10


Idealized models describe two kinds of population growth

– Exponential growth

– Logistic growth


Time

Nu

mb

er o

f in

div

idu

als

(N)

0

K

G = rN

G = rN(K – N)

K


36.5 Multiple factors may limit population growth

The logistic growth model

– Population growth slows and ceases as population density increases

– Increasing population density results in a decrease in birth rate, an increase in death rate, or both

Density of females

Clu

tch

siz

e

0 10 20 30 40 50 60 70 802.8

3.0

3.2

3.4

3.6

3.8

4.0


Abiotic factors may reduce population size before other limiting factors become important


Apr May Jun Jul Aug Sep Oct Nov Dec

Nu

mb

er o

f ap

hid

s

Exponentialgrowth

Suddendecline


Most populations fluctuate in numbers


Time (years)

Nu

mb

er o

f fe

mal

es

1975 1980 1985 1990 1995 20000

20

40

60

80


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

Some populations fluctuate in density with regularity

Boom-and-bust cycles

– Food shortages

– Predator-prey interactions

Lynx

Snowshoe hare

Ly

nx

po

pu

lati

on

siz

e(t

ho

usa

nd

s)

Ha

re p

op

ula

tio

n s

ize

(th

ou

san

ds)

Year1850 1875 1900 1925

0

40

80

120

160

0

3

6

9


36.7 EVOLUTION CONNECTION: Evolution shapes life histories

Life history

– Series of events from birth to death

r/K selection

– r-selective traits

– K-selective traits

Males Females

Experimentaltransplant ofguppies

Predator: Killifish; preysmainly on small guppies

Guppies:Larger atsexual maturitythan those inpike-cichlid pools

Pools with killifish,but no guppies priorto transplant

Predator: Pike-cichlid preys mainly on large guppies

Guppies: Smaller at sexual maturity thanthose in killifish pools11 years

later

Mas

s o

f g

up

pie

sat

mat

uri

ty (

mg

)

40

80

120

160

200

67.5 76.1

161.5185.6

Ag

e o

f g

up

pie

sat

mat

uri

ty (

day

s)

Males Females

20

40

60

80100

48.558.2

85.792.3 Control:Guppies from poolswith pike-cichlidsas predators

Experimental:Guppies transplantedto pools with killifishas predators

Predator: Killifish; preysmainly on small guppies

Experimentaltransplant ofguppies

Guppies:Larger atsexual maturitythan those inpike-cichlid pools

Pools with killifish,but no guppies priorto transplant

Predator: Pike-cichlid preys mainly on large guppies

Guppies: Smaller at sexual maturity thanthose in killifish pools

Males Females

Mas

s o

f g

up

pie

sat

mat

uri

ty (

mg

)

Males Females

4080

120160200

67.5 76.1

161.5185.6

Ag

e o

f g

up

pie

sat

mat

uri

ty (

day

s)

2040

60

80100

48.558.2

85.7 92.3 Control:Guppies from poolswith pike-cichlidsas predators

Experimental:Guppies transplantedto pools with killifishas predators

11 yearslater


36.8 CONNECTION: Principles of population ecology have practical applications

Sustainable resource management

– Maximum sustained yield

1960

Yie

ld (

tho

usa

nd

s o

f m

etri

c to

ns)

1970 1980 1990 20000

100

200

300

400

500

600

700

800

900


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

Human population is expected to continue increasing for several decades

95% of the increase is in developing nations

1500

Year

Population increase

Total population size

To

tal p

op

ula

tio

n (

in b

illio

ns

)

1550 1600 1650 1700 1750 1800 1850 1900 1950 2000 20500

2

4

6

8

10

20

40

60

80

100

An

nu

al in

cre

ase

(in

mill

ion

s)

Year

Birth rateDeath rate

Rate of increase (r)

1900 19501925 1975 2000 2025 20500

10

20

30

40

50

Bir

th o

r d

eath

rat

ep

er 1

,000

po

pu

lati

on


Population momentum of Mexico

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

0 1 2 3 4 55 4 3 2 1 0 1 2 3 4 55 4 3 2 1

1980

Age

Male Female

80+75-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-14

5-90-4

Population in millionsTotal population size = 68,347,479


FemaleMale

2005 2030

FemaleMale


0 1 2 3 4 55 4 3 2 1

Age

80+75-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-14

5-90-4

5 4 3 2 1 0 1 2 3 4 5Population in millions

Total population size = 68,347,479

1980

Male Female

5 4 3 2 1 0 1 2 3 4 5

Age

80+75-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-14

5-90-4


FemaleMale

2005

5 4 3 2 1 0 1 2 3 4 5

Age

80+75-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-14

5-90-4

2030

FemaleMale



36.10 CONNECTION: Age structures reveal social and economic trends

Age structure diagram

– Reveals a population’s growth trends

Age1980

Birth years Male Female2005 2030

Birth years Male Female Birth years Male Female80+ before 1900 before 1926 before 1951

1951-551926-301901-190575-7970-74 1906-10 1931-35 1956-60

1961-651936-401911-1565-6960-6455-59

1916-20 1941-45 1966-701971-751946-501921-25

50-54 1926-30 1951-55 1976-801981-851956-601931-3545-49

40-44 1936-40 1961-65 1986-901991-951966-701941-4535-39

30-34 1946-50 1971-75 1996-20002001-051976-801951-5525-29

20-24 1956-60 1981-85 2006-102011-151986-901961-6515-19

10-14 1966-70 1991-95 2016-202021-251996-20001971-755-9

0-4 1976-80 2001-2005 2026-30

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

Total population size = 363,811,435Population in millions


12 10 8 6 4 2 0 2 4 6 8 10 1212 10 8 6 4 2 0 2 4 6 8 10 12Population in millions



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

U.S. Census Bureau projection

– 8 billion people within the next 20 years

– 9.5 billion by mid-21st century


Ecological footprint helps understand resource availability and usage

The United States has a

– Big ecological footprint

– Large ecological deficit

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


You should now be able to

1. Explain the factors that determine the characteristics of a population

2. Describe exponential growth and the factors that produce logistic growth of a population

3. Explain the limiting factors that influence population growth

4. Distinguish between r- and K-strategies

5. Describe and give examples of the different types of life histories


6. Explain the factors the determine human population growth

7. Describe the concept of ecological footprint

You should now be able to

Chapter 36

Documents

population densitiescopyright

pearson education

fishes population ecology

population size factors

area dispersion patterns

number of individuals

way individuals

random pattern of dispersion