organism
population
community
ecosystem
biosphere
Population Ecology
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Energy flows through ecosystems
sun
secondary
consumers
(carnivores)
primary consumers
(herbivores)
producers (plants)
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loss of
energy
loss of
energy
Food chains
 Trophic levels
feeding relationships
 start with energy from
the sun
 captured by plants



1st
sun
top carnivore
Level 3
Secondary consumer
carnivore
Level 2
Primary consumer
heterotrophs
herbivore
level of all food chains
food chains usually go Level 1
Producer
up only 4 or 5 levels
 inefficiency of energy
transfer

Level 4
Tertiary consumer
all levels connect to
decomposers
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autotrophs
Decomposers
Bacteria
Fungi
sun
Inefficiency of energy transfer
 Loss of energy between levels of food
chain

To where is the energy lost? The cost of living!
17%
growth
only this energy
moves on to the
next level in
the food chain
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energy lost to
daily living
33%
cellular
respiration
50%
waste (feces)
sun
Ecological pyramid
 Loss of energy between levels of food
chain

can feed fewer animals in each level
1
100
100,000
1,000,000,000
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Humans in food chains
 Dynamics of energy through ecosystems have
important implications for human populations
 how much energy does it take to feed a human?
 if we are meat eaters?
 if we are vegetarian?
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Food webs
 Food chains are

linked together into
food webs
Who eats whom?

a species may
weave into web at
more than one level
 bears
 humans
 eating meat?
 eating plants?
AP Biology
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
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?
AP Biology
Why do teenage boys pay high car insurance rates?
Demography
 Factors that affect growth & decline of
populations

vital statistics & how they change over time
Life table
females
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males
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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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
AP Biology
Natural selection
favors a life
history that
maximizes lifetime
reproductive
success
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
Logistic rate of growth
 Can populations continue to grow
exponentially? Of course not!
no natural controls
K=
carrying
capacity
effect of
natural controls
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

varies with changes
in resources
Every species has a
diff. CC
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
AP Biology
0
10
20
30
40
Time (days)
50
60
Imagine Your Fridge
Your fridge is like all
of the resources
(food, water, free
space) in an
ecosystem.
What if we want to
throw a party?
AP Biology
Imagine Your Fridge
The fridge won’t replenish magically, and I
don’t have the money to keep putting food in
the fridge forever.
So too many guests means that…
So too many animals means that…
Someone goes hungry…
Not enough food/water/free
space…
And leaves the party. 
And organisms die. 
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Carrying Capacity
 Key Point #2: We can read a carrying
capacity graph to predict changes in
population size
Population size
Dotted line = Carrying Capacity
Graph line = Population
size at a specific time
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Time
Carrying Capacity
Population size
Time
 When a population is BELOW its carrying
capacity, it will INCREASE in size
 Birth rate exceeds death rates
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Carrying Capacity
Population size
Time
 But if it increases too much and rises ABOVE its
carrying capacity, it will DECREASE in size
 Death rate exceeds birth rate
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Carrying Capacity
Population size
Time
 When a population is BELOW its carrying
capacity, it will INCREASE in size
 Birth rate exceeds death rates
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Carrying Capacity
Population size
Time
 This happens over and over… but the increases
and decreases get smaller and smaller…
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Carrying Capacity
Population size
Time
 Until eventually, the population size BECOMES

STABLE AT THE CARRYING CAPACITY
Birth rate = death rate
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Changes in Carrying Capacity
 Population cycles

predator – prey
interactions
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?
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
the world takes…
World total
the effect of income
& education
Developing countries
3
2
1
0
1900
AP Biology
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
AP Biology
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