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
Why Population Ecology?
 Scientific goal

understanding the factors that influence the
size of populations
 general principles
 specific cases
 Practical goal

management of populations
 increase population size
 endangered species
 decrease population size
 pests
 maintain population size
 fisheries management

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maintain & maximize sustained yield
Factors that affect Population Size
 Abiotic factors



sunlight & temperature
precipitation / water
soil / nutrients
 Biotic factors

other living organisms
 prey (food)
 competitors
 predators, parasites,
disease
 Intrinsic factors

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adaptations
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

abiotic & biotic factors
 temperature, rainfall, food, predators, etc.

habitat
adaptations to
polar biome
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adaptations to
rainforest biome
Changes in range
 Range expansions & contractions

changing environment
aspen
oak, maple
15,000 years ago
glacial period
Alpine tundra
Elevation (km)
3 km
Spruce-fir forests
white birch
Alpine tundra
sequoia
Present
Spruce-fir forests
Mixed conifer forest
Woodlands
2 km
Mixed conifer forest
1 km
Woodlands
Grassland,
chaparral, and
desert scrub
Grassland, chaparral,
0 km
AP
Biology and desert scrub
result of competition
At risk populations
 Endangered species

limitations to range / habitat
 places species at risk
Devil’s hole
pupfish
Iiwi
Hawaiian
bird
Socorro
isopod
Iriomote cat
New Guinea
tree
kangaroo
Catalina
Island
mahogany
tree
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Northern white rhinoceros
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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Why do teenage boys pay high car insurance rates?
Demography
 Factors that affect growth & decline of
populations

Life table
vital statistics & how they change over
time
females
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males
What adaptations have
led to this difference
in male vs. female
mortality?
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
AP Biology
Age structure
 Relative number of individuals of each age
What do these data imply about population growth
in these countries?
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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
AP Biology
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
 age at first reproduction
 investment per offspring
 number of reproductive cycles per lifetime
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Natural selection
favors a life
history that
maximizes lifetime
reproductive
success
Parental survival
Kestrel Falcons:
The cost of larger
broods to both male
& female parents
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Reproductive strategies
 K-selected



late reproduction
few offspring
invest a lot in raising offspring
 primates
 coconut
 r-selected



K-selected
early reproduction
many offspring
little parental care
 insects
 many plants
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r-selected
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
Population growth
change in population = births – deaths
Exponential model (ideal conditions)
dN = riN
growth increasing at constant rate
dt
N
r
ri
t
d
= # of individuals
= rate of growth
= intrinsic rate
= time
= rate of change
intrinsic rate =
maximum
rate of growth
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every pair has
4 offspring
every pair has
3 offspring
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
marking territory
= competition
 Limiting factors

density dependent
 competition: food, mates,
nesting sites
 predators, parasites,
pathogens

density independent
 abiotic factors
 sunlight (energy)
 temperature
 rainfall
APcompetition
Biology
for nesting sites
swarming locusts
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 Shell
~2 months


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ecological & economic damage

reduces diversity
loss of food & nesting sites
for animals
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
Changes in Carrying Capacity
 Population cycles

predator – prey
interactions
At what
population level is the
carrying capacity?
K
K
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Population of…
China: 1.3 billion
India: 1.1 billion
Human population growth
Doubling times
250m  500m = y ()
500m  1b = y ()
1b  2b = 80y (1850–1930)
2b  4b = 75y (1930–1975)
What factors have contributed to
this exponential growth pattern?
Is the human
population reaching
carrying capacity?
adding 82 million/year
~ 200,000 per day!
20056 billion
Significant advances
in medicine through
science and technology
Industrial Revolution
Bubonic plague "Black Death"
1650500 million
AP Biology
Distribution of population growth
World population in billions
11
uneven distribution
of population:
10 are in developing countries
90% of births
9
uneven distribution of resources:
8 consumes ~90%
wealthiest 20%
of resources
There
are choices as
increasing gap
poor
which future path
7 between rich & to
6
5
4
3
the world takes…
World total
the effect of income
What is K
& education
for humans?
10-15 billion?
Developing countries
2
1
0
1900
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Developed countries
1950
Time
2000
2050
Ecological Footprint
USA
30.2
Germany
15.6
over-population or
over-consumption?
Brazil
6.4
Indonesia
3.7
Nigeria
3.2
India
2.6
0 2 4
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uneven distribution:
wealthiest 20% of world:
86% consumption of resources
53% of CO2 emissions
6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
Acres
Amount of land required to support an
individual at standard of living of population
Ecological Footprint
deficit
surplus
Based on land & water area
used to produce all resources
each country consumes & to
absorb all wastes it generates
AP Biology
Measuring population density
 How do we measure how many
individuals in a population?
number of individuals in an area
 mark & recapture methods

Difficult to count a moving target
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sampling populations
Evolutionary adaptations
 Coping with environmental variation

regulators
 endotherms
 homeostasis
 (“warm-blooded”)

conformers
 ectotherms
 (“cold-blooded”)
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Bright blue marble spinning in space
Ecology
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Studying organisms in their environment
organism
population
community
ecosystem
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biosphere
Any
Questions?
AP Biology
2007-2008