2. Population Dynamics
A look at the factors that tend to increase or
decrease the size of a population.
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Author -Guru
IB/ESS
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3. The population size of a species in a
given space at a given time is
determined by the interplay
between BIOTIC POTENTIAL and
ENVIRONMENTAL RESISTANCE.
Biotic potential = growth rate with
unlimited resources.
Environmental resistance = all the
factors acting jointly to limit
population growth.
5/11/2013
Author -Guru
IB/ESS
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4. POPULATION SIZE
Growth factors
(biotic potential)
Abiotic
Favorable light
Favorable temperature
Favorable chemical environment
(optimal level of critical nutrients)
Biotic
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High reproductive rate
Generalized niche
Adequate food supply
Suitable habitat
Ability to compete for resources
Ability to hide from or defend
against predators
Ability to resist diseases and parasites
Ability to migrate and live in other
habitats
Author -Guru
Ability to adapt to environmental
change
Decrease factors
(environmental resistance)
Abiotic
Too much or too little light
Temperature too high or too low
Unfavorable chemical environment
(too much or too little of critical
nutrients)
Biotic
Low reproductive rate
Specialized niche
Inadequate food supply
Unsuitable or destroyed habitat
Too many competitors
Insufficient ability to hide from or defend
against predators
Inability to resist diseases and parasites
Inability to migrate and live in other
habitats
IB/ESS
Inability to adapt to environmental
change
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5. Four variables change population
size:
1. NATALITY = birth rate
2. MORTALITY = death rate
3. IMMIGRATION = rate of organisms
moving in
4. EMIGRATION = rate of organisms
moving out
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Author -Guru
IB/ESS
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7. Opportunistic or r-Selected Species
cockroach
dandelion
Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching reproductive age
Small adults
Adapted to unstable climate and environmental
conditions
High population growth rate (r)
Population size fluctuates wildly above and below
carrying capacity (K)
Generalist niche
Low ability to compete
Early successional species
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Author -Guru
IB/ESS
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8. Competitor or K-Selected Species
elephant
saguaro
Fewer, larger offspring
High parental care and protection of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental
conditions
Lower population growth rate (r)
Population size fairly stable and usually close
to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species
5/11/2013
Author -Guru
IB/ESS
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11. DENSITY INDEPENDENT FACTORS = affect a
populations’ size regardless of its population density.
1. Weather
2. Earthquakes
3. Floods
4. Fires
. . . Natural disasters
R-strategists populations are
most affected by these.
5/11/2013
Author -Guru
IB/ESS
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12. DENSITY DEPENDENT FACTORS = affect a
populations’ size depending on its population density.
1. Predation
2. Disease
3. Availability of food and water
4. Space
Negative Feedback!!
5/11/2013
Author -Guru
IB/ESS
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13. INTERNAL FACTORS = might include densitydependent fertility or size of breeding
territory.
EXTERNAL FACTORS = might include
predation and disease.
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Author -Guru
IB/ESS
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14. Species interactions influence population
growth and carrying capacity =
SYMBIOSIS
Competition for resources.
High
Relative population density
Relative population density
High
Paramecium
aurelia
Paramecium
caudatum
Low
0
2
4
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6
8
10
Days
12
14
16
18
Author -Guru
Each species grown alone
Low
0
Paramecium
aurelia
Paramecium
caudatum
2
4
6
8 10
Days
12
14
16
IB/ESS Both species grown together 14
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17. Avoiding predators
Span worm
Wandering leaf insect
Poison dart frog
Viceroy butterfly mimics
monarch butterfly
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Author -Guru
Bombardier beetle
Hind wings of io moth
resemble eyes of a
much larger animal
IB/ESS
Foul-tasting monarch
butterfly
When touched, the
snake caterpillar
changes shape to look
like the head of a snake
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