Copyright © 2009 Pearson Education, Inc. POPULATION STRUCTURE AND DYNAMICS

Copyright © 2009 Pearson Education, Inc.

POPULATION STRUCTURE AND DYNAMICS


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


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

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: populations with rapid growth and maturation; little postnatal care; also known as “opportunistic populations”

– K-selective traits: populations with a roughly constant size whose members have low reproductive rates. Lots of postnatal care required. “K” = Kids!


THE HUMAN POPULATION


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

Total population size = 295,734,134

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

Total population size = 227,726,463


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

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Copyright © 2009 Pearson Education, Inc. POPULATION STRUCTURE AND DYNAMICS