03 Pop Eco IB Bio Cblogs.4j.lane.edu/sanderson/files/2017/09/Notes_Pop-Eco_IB-Bio-C.pdf · Population • A population • Is a group of individuals of a single species living in

POPULATION ECOLOGYCh 40 (Urry)

© 2014 Pearson Education, Inc.

Concept 40.4: Population density, dispersion, and demographics

▪ biotic and abiotic factors influence density, distribution, and size of populations

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

Population size• 4 factors in pop size:

Births and immigration add individuals to a population.

Natality Immigration

PopuIation size

Emigration

Deaths

Deaths and emigration remove individuals from a population.

Population• A population

• Is a group of individuals of a single species living in the same general area• Density:• Dispersion:

• clumped• uniform• random


Life Tables• Summary of the survival pattern of a population • Follows the fate of a cohort • Age specific


Life Table: Belding’s ground squirrels• Range: E. OR & CA, S. ID, cent. NV,


Survivorship Curves• for Belding’s ground squirrels

– death rate is relatively constant

Figure 52.4

1000

100

10

1

Num

ber o

f sur

vivo

rs (l

og s

cale

)

0 2 4 6 8 10Age (years)

Males

Females


Figure 40.16

1,000

Percentage of maximum life span

III

Num

ber o

f sur

vivo

rs (l

og sc

ale)

100

10

01

10050

II

I


Pop Growth Rates• How fast does pop size change? • Simplest calculation:

– N = pop – t = time – B = birth – D = death∆N∆t

= B - D

∆N∆t

= bN - dN b = per capita birth rate d = per capita death rate

∆N∆t

= rN Instantaneous growth rate (r = b - d)


Population growth rate• J-curve

– under what conditions? – can it be sustained?

Figure 52.9

0 5 10 150

500

1,000

1,500

2,000

Number of generations

Pop

ulat

ion

size

(N)

dNdt

= 1.0N

dNdt

= 0.5N


Figure 40.18

6,000

Year

Elep

hant

pop

ulat

ion

0

2,000

8,000

4,000

1900 1930 1940 1950 1960 19701910 1920


Logistic Growth• Carrying capacity (K)

– = maximum pop size the env. can support

• Use logistic growth model


Logistic Growth model• Sigmoid (S-shaped) curve

Figure 52.12

dNdt

= 1.0N Exponential growth

Logistic growth

dNdt

= 1.0N1,500 − N

1,500

K = 1,500

0 5 10 150

500

1,000

1,500

2,000

Number of generations

Pop

ulat

ion

size

(N)


The Logistic Model and Life Histories• 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


Regulation of Pop Size• complex interaction of biotic and abiotic

influences • Two general questions:

– What factors stop a population from growing? – Why do some populations show radical

fluctuations in size over time, while others remain stable?


Density-Dependent Population Regulation• Density-dependent birth and death rates

– Competition for resources – health (disease) – predation – toxic wastes


Population Cycles• Many populations

– Undergo regular boom-and-bust cycles

Figure 52.21 Year1850 1875 1900 1925

0

40

80

120

160

0

3

6

9

Lynx

pop

ulat

ion

size

(th

ousa

nds)

Har

e po

pula

tion

size

(th

ousa

nds)

Lynx

Snowshoe hare


Human Pop Growth• What is our growth curve? • What’s going on with our growth rate? • No population can grow indefinitely

– humans are no exception


The Global Human Population• The human population

– Increased relatively slowly until about 1650 and then began to grow exponentially

Figure 52.228000 B.C.

4000 B.C.

3000 B.C.

2000 B.C.

1000 B.C.

1000 A.D.

0

The Plague Hum

an p

opul

atio

n (b

illio

ns)

2000 A.D.

0

1

2

3

4

5

6


• Though the global population is still growing – The rate of growth began to slow approximately

40 years ago

Figure 52.231950 1975 2000 2025 2050

Year

2003

Per

cent

incr

ease

2.2

2

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

0

1.8


Regional Patterns of Population Change• To maintain population stability

– A regional human population can exist in one of two configurations • High birth rate, high death rate • Low birth rate, low death rate


Demographic Transition• = the move from the first toward the second state

Figure 52.24

50

40

20

0

30

10

1750 1800 1850 1900 1950 2000 2050

Birth rateDeath rate

Birth rateDeath rate

Year

Sweden Mexico

Birt

h or

dea

th ra

te p

er 1

,000

peo

ple


Age structure• the relative number of individuals at each age • Is commonly represented in pyramids

Figure 52.25

Rapid growth Afghanistan

Slow growth United States

Decrease Italy

Male Female Male Female Male FemaleAge Age

8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8Percent of population Percent of population Percent of population

80–8485+

75–7970–7465–6960–6455–5950–5445–4940–4435–3930–34

20–2425–29

10–145–90–4

15–19

80–8485+

75–7970–7465–6960–6455–5950–5445–4940–4435–3930–34

20–2425–29

10–145–90–4

15–19


Global Carrying Capacity• Just how many humans can the biosphere

support? • $64k question


Ecological Footprint• The ecological footprint concept

– Summarizes the aggregate land and water area needed to sustain the people of a nation

– Is one measure of how close we are to the carrying capacity of Earth


• Ecological footprints for 13 countries – Show that the countries vary greatly in their footprint

size and their available ecological capacity

Figure 52.27

16

14

12

10

8

6

4

2

00 2 4 6 8 10 12 14 16

New Zealand

AustraliaCanada

Sweden

WorldChina

India

Available ecological capacity (ha per person)

SpainUK

Japan

GermanyNetherlands

Norway

USA

Eco

logi

cal f

ootp

rint (

ha p

er p

erso

n)


• At more than 6 billion people – The world is already in ecological deficit


Stability and Fluctuation• Long-term population studies

– Isle Royale moose first migrated to island c. 1900

Documents

03 Pop Eco IB Bio Cblogs.4j.lane.edu/sanderson/files/2017/09/Notes_Pop-Eco_IB-Bio-C.pdf · Population • A population • Is a group of individuals of a single species living in