2.6.1 .2
DESCRIPTION
TRANSCRIPT
2.6.1-.2 Populations
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Population Growth
change in the size of a population over time.
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• POPULATION = a group of interbreeding organisms (same species) that live in the same place at the same time and compete for the same resources.
• Resources = food, water, shelter, mates, and so on . . .
• resources pop. size
• resources pop. size
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Populations change in response to environmental stress or changes in environmental conditions.
1. In size = # of individuals
2. Density = # of individual / specific space
3. Age distribution = proportions / age group
4. Dispersion =
Clumped
(elephants)
Uniform
(creosote bush)
Random
(dandelions) 5/11/2013 Author-Guru IB/ESS 4
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No population can grow indefinitely!
Every environment has a CARRYING
CAPACITY = the maximum number of
individuals of a given species that
can be sustained indefinitely in
a given space. 2.0
1.5
1.0
.5
Nu
mb
er
of
sh
eep
(m
illio
ns)
1800 1825 1850 1875 1900 1925
Year
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Factors that affect carrying capacity:
1. Competition with/in and between
species.
2. Natural and human caused catastrophes.
3. Immigration and emigration.
4. Seasonal fluctuations in food, water,
shelter, and nesting sites.
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A population that has few if any resource
limitations grows exponentially.
EXPONENTIAL GROWTH starts out slowly
and then proceeds faster and faster as the
population increases.
Time (t)
Po
pu
lati
on
siz
e (
N) “J” population
growth curve
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Bacteria population
8 1024
24 hours
later
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LOGISTIC GROWTH involves initial exponential
growth and then there is a steady decrease in
growth as the population encounters
environmental resistance and approaches
carrying capacity and
levels off.
“S or sigmoid”
population growth
curve
Time (t)
Po
pu
lati
on
siz
e (
N)
K
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Time (t)
Po
pu
lati
on
siz
e (
N)
K
Exponential phase
Transitional phase
Plateau phase
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2,000
1,500
Nu
mb
er
of
rein
deer
1910 1920 1930 1940 1950
Year
1,000
500
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Kaibab Plateau
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Kaibab Plateau
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