Download Population Growth

BIOLOGY CHAPTER 5
POPULATIONS
SECTION 1. HOW
POPULATIONS GROW
Edited for Keystone content emphasis
The study of population increases
and decreases is called population
dynamics.
Population Growth
Three factors can affect population
size:
• the number of births
• the number of deaths
• the number of individuals that enter or
leave the population
A population can grow when its
birthrate is greater than its death rate.
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Exponential Growth
Under ideal conditions with unlimited
resources, a population will grow
exponentially.
Exponential growth occurs when the
individuals in a population reproduce at a
constant rate.
The population becomes larger and
larger until it approaches an infinitely
large size.
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Exponential Growth
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Logistic Growth
As resources become less available,
the growth of a population slows or
stops.
Logistic growth occurs when a
population's growth slows or stops
following a period of exponential
growth.
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Logistic growth is characterized by
an S-shaped curve.
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SECTION 2.
LIMITS TO GROWTH
Limiting Factors
• The primary productivity of an
ecosystem can be reduced when
there is an insufficient supply of a
particular nutrient.
• Ecologists call such substances
limiting nutrients.
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• A limiting nutrient is an example of
a more general ecological concept:
a limiting factor.
• In the context of populations, a
limiting factor is a factor that
causes population growth to
decrease.
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Examples:
• Growth of the population of a
predator is limited by the amount of
prey.
• Availability of sunlight limits the
growth of phytoplankton in the
deep ocean.
The largest size population that can
be supported by the ecosystem is
the carrying capacity.
A population may temporarily grow
past the carrying capacity, but this
cannot be sustained; eventually a
resource will run out and it must
decrease back to the carrying
capacity.
The carrying capacity can change if
conditions change.
Example: elimination of predators
such as wolves can increase the
ecosystem’s carrying capacity for
deer.
Predation
Populations in nature are often
controlled by predation.
The regulation of a population by
predation takes place within a
predator-prey relationship, one of
the best-known mechanisms of
population control.
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Ex. - hare and lynx in Northern Canada
• Prey population decreases, less food
for predators. They decrease.
• Prey population can then increase.
• This gives more food for predators, so
they increase, etc.
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The wolves and moose of Isle
Royale in Lake Superior have been
studied since 1958
Wolf and Moose Populations on Isle Royale
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