Factors%20Affecting%20Population%20Change

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Factors Affecting Population Change

• Density-dependent factors limit population growth
  and intensify as the population increases in size
  (i.e. Competition for resources, disease...)

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Density-dependent factors

• Intraspecific competition is when individuals of
  the same species compete for resources. If this
  is high then the population will have a low
  growth rate.

3
Density-dependent factors

• Predation is the consumption of prey by a
  predator. If there is more prey available they
  will be chosen more by predators.

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Density-dependent factors

• Allee effect Warder Allee found that some
  density-dependent factors reduce population
  growth when the population is at a low density
  rather than high density.
• Ex. harder for individuals to find a mate and
  successfully reproduce thus lowering the growth
  rate of species.

5
Allee-effect continued

• Small populations also may go through inbreeding
  depression which reduces the populations' genetic
  variability and may prevent successful population
  growth.

6
Allee-effect continued

• The minimum viable population size is the
  smallest number of individuals that ensures the
  population will persist for a certain period of
  time.
• Allows biologists to determine whether a species
  is endangered.

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Factors Affecting Population Change

• Density-independent factors limit population
  growth no matter what the population size
• i.e. Natural disaster, human intervention...

8
Density-independent factors

• The resource in the ecosystem that is in the
  shortest supply is known as the limiting factor
  since it is preventing massive population growth.

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Population Change Affects the Entire Ecosystem

• A change in one population of species can affect
  the entire hierarchy of living things in that
  ecosystem.
• Ex. The disappearance of beaver from this
  ecosystem causes a decrease in the wolf
  population which would cause an increase in its
  other prey