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organism
population
community
ecosystem
biosphere
Population Ecology
AP Biology
Life takes place in populations
 Population

group of individuals of same species in
same area at same time
 rely on same
resources
 interact
 interbreed
AP Biology Ecology: What factors affect a population?
Population
Characterizing a Population
 Describing a population
population range
 pattern of spacing

 density

size of population
1970
1966
1964
1960
1965
1961
Equator
1958
1951
1943
1937
1956
1970
Immigration
from Africa
~1900
range
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density
Population Range
 Geographical limitations

biotic & abiotic factors
 food, predators, temperature, rainfall, etc.

habitat
adapted to polar region
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adapted to rainforest
Population Spacing
 Dispersal patterns within a population
Provides insight into the
environmental associations
& social interactions of
individuals in population
clumped
random
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uniform
Clumped Pattern
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(most common)
Uniform
May result from
direct
interactions
Clumped
patterns
between individuals
in the population
 territoriality
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Population Size
 Changes to
population size

adding & removing
individuals from a
population
 birth
 death
 immigration
 emigration
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Population growth rates
 Factors affecting population growth rate

sex ratio
 how many females vs. males?

generation time
 at what age do females reproduce?

age structure
 how females at reproductive age in cohort?
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Age structure
 Relative number of individuals of each age
What do the data imply about population growth in
these countries?
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Survivorship curves
 Graphic representation of life table
The relatively straight lines of the plots indicate relatively constant
rates of death; however, males have a lower survival rate overall
than females.
Belding ground squirrel
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Survivorship curves
 Generalized strategies
Survival per thousand
1000
Human
(type I)
Hydra
(type II)
What do these graphs
tell about survival &
strategy of a species?
I. High death rate in
post-reproductive
years
100
II. Constant mortality
rate throughout life
span
Oyster
(type III)
10
1
0
25
50
75
Percent of maximum life span
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100
III. Very high early
mortality but the
few survivors then
live long (stay
reproductive)
Trade-offs: survival vs. reproduction
 The cost of reproduction

increase reproduction may decrease
survival
 investment per offspring
 reproductive events per lifetime
 age at first reproduction
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Natural selection
favors a life
history that
maximizes lifetime
reproductive
success
Trade offs
Number & size of offspring
vs.
Survival of offspring or parent
r-selected
K-selected
“Of course, long before you mature,
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most of you will be eaten.”
Life strategies & survivorship curves
K-selection
Survival per thousand
1000
Human
(type I)
Hydra
(type II)
100
Oyster
(type III)
10
r-selection
1
0
25
50
75
Percent of maximum life span
AP Biology
100
Exponential growth rate
 Characteristic of populations without
limiting factors

introduced to a new environment or rebounding
from a catastrophe
Whooping crane
coming back from near extinction
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African elephant
protected from hunting
Regulation of population size
 Limiting factors

density dependent
 food supply, competition
 predators
 disease

density independent
 abiotic factors
 sunlight
 temperature
 rainfall
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Introduced species
 Non-native species


transplanted populations grow
exponentially in new area
out-compete native species
 loss of natural controls
 lack of predators, parasites,
competitors


reduce diversity
examples
 African honeybee gypsy moth
 gypsy moth
 zebra mussel
 purple loosestrife
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kudzu
Zebra mussel
~2 months
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ecological & economic damage
Purple loosestrife
1968
1978


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reduces diversity
loss of food & nesting sites
for animals
Logistic rate of growth
 Can populations continue to grow
exponentially? Of course not!
no natural controls
K=
Carrying
capacity
What happens as
N approaches K?
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effect of
natural controls

varies with
changes in
resources
What’s going
on with the
plankton?
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10
8
6
4
2
0
1915
1925
1935
1945
Time (years)
Number of cladocerans
(per 200 ml)
population size
that environment
can support with
no degradation
of habitat
Number of breeding male
fur seals (thousands)
Carrying capacity
 Maximum
500
400
300
200
100
0
0
10
20
30
40
Time (days)
50
60
 K-selection

density dependent selection for traits such as competitive
ability and efficient resource utilization

late reproduction
few offspring but invest a lot in raising offspring

 primates
 coconut
 r-selection

density independent selection for traits that maximize
population growth such as increased fecundity (fertility)
and early maturity

early reproduction
many offspring but little parental care

 insects
 many plants
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Changes in Carrying Capacity
 Population cycles

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predator – prey
interactions