3. • 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 . . .
•
pop. size
•
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resources
resources
pop. size
Author-Guru
IB/ESS
3
4. 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 =
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Clumped
(elephants)
Uniform
Author-Guru
IB/ESS
(creosote bush)
Random
(dandelions)
4
6. No population can grow indefinitely!
Number of sheep (millions)
Every environment has a CARRYING
CAPACITY = the maximum number of
individuals of a given species that
can be sustained
indefinitely in
2.0
a given space.
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1.5
1.0
.5
Author-Guru
1800 IB/ESS
1825
1850
1875
Year
1900
1925 6
7. 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.
5/11/2013
Author-Guru
IB/ESS
7
8. 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.
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Population size (N)
“J” population
growth curve
Author-Guru
IB/ESS
Time (t)
8
11. 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
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Author-Guru
Population size (N)
K
IB/ESS
Time (t)
11
