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organism
population
community
ecosystem
biosphere
Population Ecology
AP Biology
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
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
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 Dispersion
 Density of population

 #individuals per unit area
1970
1966
1964
1960
1965
1961
Equator
1958
1951
1943
1937
1956
1970
Immigration
from Africa
~1900
range
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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
Population Dispersion
 Spacing patterns within a population
Provides insight into the
environmental associations
& social interactions of
individuals in population
clumped
Why clump?
random
Why uniform?
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uniform
Why random?
Population Size
 Changes to
population size
can occur by:
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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
 #females at reproductive age in cohort?
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Why do teenage boys pay high car insurance rates?
Demography
 Study of a populations vital statistics and
how they change over time

Life table
Life tables, Age Structure Diagrams and Survivorship
Graphs
females
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males
What adaptations have
led to this difference
in male vs. female
mortality?
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
 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
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

To increase reproduction may decrease
survival: (think about…)
 age at first reproduction
 investment per offspring
 number of reproductive cycles per lifetime
 parents not equally invested
Natural selection
 offspring mutations
favors a life history
 Life History determined by costs
that maximizes
lifetime
and benefits of all adaptations.
reproductive
success
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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.”
Survivorship Curves with Reproductive Strategy
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 Rate Models
 Exponential growth
Rapid growth
 No constraints

 Logistic growth
Environmental constraints
 Limited growth

AP Biology
Population Growth Math
 Change in population = Births – Deaths





Per capita birth rate = b
Per capita death rate = d
# of individuals = N
Rate of population growth (r) = b – d
Survivorship = % surviving
Ex: If there are 50 deer in a population, 13 die and 27 are born the next
month. What is the population size the following month?

(Answer: 27-13 = 14, so new population is 64)
Ex: What is the birth rate for the deer? #Births/N = b
 Answer: 27/50 = .54
 Death rate (d) = 13/50 = .26
Ex: What is the rate of growth for the deer? r = .54 -.26 = .28
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Exponential Growth (ideal conditions)
 No environmental barriers
 Growth is at maximum rate
dN/dt = RmaxN
N = # individuals
Rmax = growth rate
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Exponential Growth
 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
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
Logistic Growth Equation
dN/dt = rmaxN(K-N)/K
K = carrying capacity of population
Ex: If a population has a carrying capacity of 900 and the rmax
is 1, what is the population growth when the population is
435? 1 x 435 (900-435)/900 = 224
What if the population is at 850?
What if it is at 1010?
Explain the results of each problem.
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
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
K
K
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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 (INVASIVE)




transplanted populations grow
exponentially in new area
out-compete native species
reduce diversity
examples
 African honeybee
 gypsy moth
gypsy moth
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kudzu
Zebra musselssel
~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
Any
Questions?
AP Biology
2007-2008