You are an ecologist. Devise a method of estimating the number of great blue heron in Rhode Island.

• Mark-recapture method– Scientists capture, tag, and release a random

sample of individuals (s) in a population

– Marked individuals are given time to mix back into the population

– Scientists capture a second sample of individuals (n), and note how many of them are marked (x)

– Population size (N) is estimated by

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snx

N

LECTURE PRESENTATIONSFor CAMPBELL BIOLOGY, NINTH EDITION

Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson

© 2011 Pearson Education, Inc.

Lectures byErin Barley

Kathleen Fitzpatrick

Population Ecology

Chapter 53

Bioflix: population ecology

AP biology test formula sheet

Patterns of dispersion within a population's geographic range.

(a) Clumped

(b) Uniform

(c) Random

What pieces of information can you glean from the life table data?

What pieces of information can you glean from the life table data?

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

© 2011 Pearson Education, Inc.

Figure 53.5

Males

Females

1,000

100

10

1

Age (years)

Nu

mb

er o

f su

rviv

ors

(lo

g s

cale

)

0 2 4 6 8 10

• Survivorship curves can be classified into three general types

– Type I: low death rates during early and middle life and an increase in death rates among older age groups

– Type II: a constant death rate over the organism’s life span

– Type III: high death rates for the young and a lower death rate for survivors

• Many species are intermediate to these curves

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Figure 53.6

1,000

III

II

I

100

10

1100500

Percentage of maximum life span

Nu

mb

er o

f su

rviv

ors

(lo

g s

cale

)

Reproductive Rates

• For species with sexual reproduction, demographers often concentrate on females in a population

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

• It describes the reproductive patterns of a population

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Table 53.2

How would an ecologist determine change in population size over a given period of time?

Devise a formula.

Population dynamics

Births Deaths

Immigration Emigration

Births and immigrationadd individuals toa population.

Deaths and emigrationremove individualsfrom 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

© 2011 Pearson Education, Inc.

Change inpopulation

sizeBirths

Immigrantsentering

populationDeaths

Emigrantsleaving

population

• The population growth rate can be expressed mathematically as

© 2011 Pearson Education, Inc.

where N is the change in population size, t is the time interval, B is the number of births, and D is the number of deaths

NB D

t

• Births and deaths can be expressed as the average number of births and deaths per individual during the specified time interval

© 2011 Pearson Education, Inc.

where b is the annual per capita birth rate, m (for mortality) is the per capita death rate, and N is population size

B bND mN

• The population growth equation can be revised

© 2011 Pearson Education, Inc.

NbN mN

t

• The per capita rate of increase (r) is given by

© 2011 Pearson Education, Inc.

r b m

• Zero population growth (ZPG) occurs when the birth rate equals the death rate (r 0)

• Change in population size can now be written as

Nt

rN

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• Instantaneous growth rate can be expressed as

dNdt

rinstN

© 2011 Pearson Education, Inc.

• where rinst is the instantaneous per capita rate of increase

Exponential Growth

• Exponential population growth is population increase under idealized conditions

• d means discrete, or over a short period of time• Under these conditions, the rate of increase is at its

maximum, denoted as rmax

• The equation of exponential population growth is

© 2011 Pearson Education, Inc.

dNdt

rmaxN

• Exponential population growth results in a J-shaped curve

© 2011 Pearson Education, Inc.

Number of generations

Po

pu

lati

on

siz

e (N

)

0 5 10 15

2,000

1,500

1,000

500

dNdt

dNdt

= 1.0N

= 0.5N

Figure 53.7

The Logistic Growth Model

• In the logistic population growth model, the per capita rate of increase declines as carrying capacity is reached

• The logistic model starts with the exponential model and adds an expression that reduces per capita rate of increase as N approaches K

dNdt

(K N)

Krmax N

© 2011 Pearson Education, Inc.

Table 53.3

Number of generations

Population growthbegins slowing here.

Exponentialgrowth

Logistic growth

Po

pu

lati

on

siz

e (

N)

0 5 1510

2,000

1,500

1,000

500

0

K = 1,500

dNdt

= 1.0N

dNdt

= 1.0N

1,500 – N1,500

( )

Figure 53.9

Figure 53.UN03

Number of generations

Po

pu

lati

on

siz

e (N

)

= rmax NdNdt

K – NK

K = carrying capacity

( )

How well do these populations fit the logistic growth model?What factor could be determining carrying capacity in each of the populations below?

Time (days) Time (days)

(a) A Paramecium population in the lab

(b) A Daphnia population in the lab

Nu

mb

er o

f P

aram

eciu

m/m

L

Nu

mb

er o

f D

aph

nia

/50

mL

1,000

800

600

400

200

00 5 10 2015 0 16040 60 80 100 120 140

180

150

120

90

60

30

0

When populationdensity is low, b > m. Asa result, the populationgrows until the densityreaches Q.

When populationdensity is high, m > b,and the populationshrinks until thedensity reaches Q.

Equilibrium density (Q)

Density-independentdeath rate (m)

Density-dependentbirth rate (b)

Population density

Bir

th o

r d

eath

rat

ep

er c

apit

a

Determining equilibrium for population density

Figure 53.16

Population size

% o

f yo

un

g s

hee

p p

rod

uci

ng

lam

bs

200 300 400 500 600

100

80

60

40

20

0

Wolves Moose

Year

Nu

mb

er o

f w

olv

es

Nu

mb

er o

f m

oo

se

1955 1965 1975 1985 1995 2005

50

40

30

20

10

0

2,500

2,000

1,500

1,000

500

0

Figure 53.18

You be the ecologist

• Hypothesis: The hare’s population cycle follows a cycle of winter food supply

• How could you test this hypothesis?

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• Hypothesis: The hare’s population cycle follows a cycle of winter food supply– If this hypothesis is correct, then the cycles

should stop if the food supply is increased– Additional food was provided experimentally to

a hare population, and the whole population increased in size but continued to cycle

– These data do not support the first hypothesis

© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.

• Hypothesis: The hare’s population cycle is driven by pressure from other predators

• How could you test this hypothesis?

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• Hypothesis: The hare’s population cycle is driven by pressure from other predators– In a study conducted by field ecologists, 90% of the

hares were killed by predators– These data support the second hypothesis

© 2011 Pearson Education, Inc.

Snowshoe hare

Lynx

Year

1850 1875 1900 1925

Nu

mb

er o

f h

ares

(th

ou

san

ds)

Nu

mb

er o

f ly

nx

(th

ou

san

ds)

160

120

80

40

0

9

6

3

0

Figure 53.19

• Hypothesis: The hare’s population cycle is linked to sunspot cycles– Sunspot activity affects light quality, which in turn affects

the quality of the hares’ food– There is good correlation between sunspot activity and

hare population size

© 2011 Pearson Education, Inc.

• The results of all these experiments suggest that both predation and sunspot activity regulate hare numbers and that food availability plays a less important role

© 2011 Pearson Education, Inc.

Inquiry: How does food availability affect emigration and foraging in a cellular slime mold?

Topsoil

Bacteria

EXPERIMENTDictyosteliumamoebas

Dictyostelium discoideum slug20

0 m

AlandIslands˚

EUROPE

Occupied patchUnoccupied patch5 km

Figure 53.21

Human population growthWhat can be said about the data?

The Plague

Hu

man

po

pu

lati

on

(b

illio

ns)

8000BCE

4000BCE

2000CE

1000BCE

2000BCE

3000BCE

1000CE

0

7

6

5

4

3

2

1

0

Projecteddata

2009

An

nu

al p

erce

nt

incr

ease

1950 1975 2000 2025 2050Year

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

Figure 53.23

Percent of population Percent of population Percent of population

Afghanistan United States Italy

Male Male MaleFemale Female FemaleAge85+

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

5–90–4

Age85+

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

5–90–4

10 0108 8 8 8 886 6 6 6 6 64 4 4 4 4 4222222 00

Match the country with the age-structure pyramid: US, Italy, Afghanistan

How do their growths compare?

Percent of population Percent of population Percent of population

Afghanistan United States Italy

Male Male MaleFemale Female FemaleAge85+

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

5–90–4

Age85+

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

5–90–4

10 0108 8 8 8 886 6 6 6 6 64 4 4 4 4 4222222 00

Futures Institute: Age-structure pyramids

Percent of population Percent of population Percent of population

Rapid growthAfghanistan

Slow growthUnited States

No growthItaly

Male Male MaleFemale Female FemaleAge85+

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

5–90–4

Age85+

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

5–90–4

10 0108 8 8 8 886 6 6 6 6 64 4 4 4 4 4222222 00

Futures Institute: Age-structure pyramids

Indus-trialized

countries

Indus-trialized

countries

Less indus-trialized

countries

Less indus-trialized

countries

Infa

nt

mo

rta

lity

(de

ath

s p

er 1

,00

0 b

irth

s)

Lif

e e

xpe

cta

nc

y (

ye

ars

)

60

50

40

30

20

10

0

80

60

40

20

0

Conclusions?

Per capita energy use

Gigajoules

> 300150–30050–15010–50< 10