Population Ecology
Population Growth
Population
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Group of organisms of the same
species living in the same place
Population Growth
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more survive than die
What are GOOD conditions for
population growth ?
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Enough food
Enough water
Enough space
Not too much disease
Not too many (efficient) predators
No serious natural disasters (examples?)
No loss of habitat
Little competition
Patterns of Population Growth
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Grows quickly at first, then
reaches a plateau
Exponential, logistic, plateau
Carrying Capacity
Maximum number of individuals of one
species that a habitat can support
Predator curve follows prey
curve in time
N1 = prey curve goes up/down first
N2 = predator curve goes up/down next
Fluctuations in Populations
Birth Rates/Death Rates/Immigration/Emigration
Invasive vs. Keystone Species
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What is an invasive species?
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What impact do invasive species have
on the environment?
Keystone Species
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What is a keystone species?
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What may happen if a keystone
species is eliminated from its
environment?
Keystone Species
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Research suggests that the number of
honey bees is declining.
–
What may be some possible causes?
– What may be possible impacts on the
environment and society if honeybees
disappear?
Exponential Population Growth
Definition: The geometric increase of a
population as it grows in an ideal,
unlimited environment.
(Campbell, Reece; Biology 6th Edition)
Some Math to Explain
Exponential Growth
Nt=Noert
Where
No= population at time 0
Nt= population at time t
e= base of natural log
r= per capita growth rate
t= observed time of growth
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Due to the doubling time of certain
organisms, such as these bacteria,
the growth rate is exponential.
Bacteriology 102 Web Site
Examples
What is one example of an organism that
comes to mind when thinking of
exponential population growth?
 Bacteria (microbes)
 Reproduce by fission every 20 minutes
under ideal laboratory conditions
 At the end of this time there would be 2
bacteria
 After 40 minutes = 4 bacteria
 After 36 hours, a bacterial mat 1 foot deep
would cover the globe.
Calculations According to
OnDarwin
the other extreme,
Charles Darwin calculated
a theoretical example
using elephants.
 On average, elephants
produce 6 young in a 100
year lifespan.
 In an ideal environment
with unlimited resources,
2 elephants could produce
a population of 19 million
in 750 years!!!!
Let’s calculate our own
problem
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RememberNt=Noert where
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Nt= population at time t
No= population at time 0
e= base of natural log
r= per capita growth rate
t= time observing growth of
organism
Daphnia-water flea
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Daphnia reproduce at 0.6/day
Start population of 100
Observe for 14 days (2 weeks)
Nt= ?
No= 100
e= natural log
r=0.6
t=14
Nt=100e^(0.6x14)
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After 14 days, our Daphnia populations has grown
exponentially to 450,000 fleas!