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All members of 1 species within defined area.
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Distribution is often determined by needs of the
organisms (food, water, mates, shelter, etc..)
 In random dispersion, the position of each individual
is independent of the others.
 Overall, dispersion depends on resource distribution.
Fig. 52.2c
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
 By contrast, uniform dispersion is when individuals are
evenly spaced.
Fig. 52.2b
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
 Clumped dispersion is when individuals aggregate in
patches.
Fig. 52.2a
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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We define a change in population size based on
the following verbal equation.
Change in population = Births during –Deaths during
size during
time interval
time interval
time interval
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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Considerations:
◦ Natality: Birth rate.
◦ Immigration: Moving in.
◦ Mortality: Death rate.
◦ Emigration: Moving out.
Populations increase when:
Natality + Immigration > Mortality +
Emigration
Fig. 52.22
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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Predictions of the human population vary from
7.3 to 10.7 billion people by the year 2050.
◦ Will the earth be overpopulated by this time?
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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a. male/female ratio
b. age distribution / 3 at reproductive age
c. species density: effects health, food & H20
supply - territory needs
d. climate, availability of shelter, predator
numbers, adaptability, means of protection
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Exponential growth
phase: Maximum
population growth
rate.
Example: Humans
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Transitional phase:
Population increases /
decreases.
Plateau phase: Steady
state. Population in
equilibrium. This is
the carrying capacity.
Carrying capacity:
Max. population size
a particular
environment can
support with no net
increase or decrease
over a long period of
time.
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Reproductive strategy where the population
puts more resources into development and
long-term survival of each individual. This
reproductive strategy is common in stable,
unchanging environments
Examples: whales, sharks, humans.
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a) long life span
b) late maturity
c) large body size
d) reproducing many times over long periods
of time.
e) one or two offspring per reproductive cycle
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Reproductive strategy where the population
puts more resources into producing as many
offspring as possible in a short period of
time. This reproductive strategy is common in
unstable or rapidly changing environments.
Examples: salmon (those that reproduce only
once), protozoa, bacteria.
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a) short life span
b) early maturity (they are capable of
reproducing very quickly)
c) small body size
d) reproduce only once
e) many offspring produced per reproductive
cycle.
*Limiting factors: factors that cause
population growth to decrease.
Affects ALL populations regardless of size.
1. Unusual weather
2. Natural disasters
3. Seasonal cycles
4. Certain human activities
Affects populations when the population reaches a
certain size.
1. Competition
- more organisms competing for the same
resource  driving force behind evolution
(those that have adaptations survive).
2. Predation
3. Parasitism/disease
** Predator always follows the
prey!