14.3 Factors Affecting Population Change

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14.3 Factors Affecting Population Change
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The role of Density

• Generally, dense populations have lower birth
  rates, higher death rates, and slower growth
  rates than less dense populations
• Density-dependant factors are factors that limit
  population growth
• 4 factors are significant disease, predation,
  parasitism and competition

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• Intraspecific competitonAs the number of
  raccoons in the forest increases, the
  availability of nesting sites limits population
  growth.
• Disease Overpopulating rabbits in Australia were
  finally controlled by a disease spread through
  the population. A higher mortality rate was
  recorded in regions with large populations than
  small populations.

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• Mangrove trees are often seen in the Florida
  everglades, their roots alternately exposed to
  the air, or submerged in water. Few tree species
  can survive such varied exposure. Mangroves can
  grow outside of the swamp, but rarely do. What
  are the ecological reasons for the unusual
  habitat of the mangrove.
• decreasing interspecific competition
• - while the swamp conditions are not optimal,
  there must be enough benefit to living where
  other trees cannot live very well
• - the advantages of more available sunlight,
  space, nutrients outweigh the disadvantages of
  immersion/exposure

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Predation

• An ecological relationship in which one animal
  kills and eats another
• Humans raise cattle for food, caring for them
  until they are slaughtered. This relationship can
  ultimately be described as predation
• Predation is beneficial to one species, but
  usually lethal to the other
• Wolves kill and eat deer. The wolves starve if no
  deer are present. The deer overpopulate and
  starve if their numbers increase. The
  relationship between wolves and deer is predation

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The minimum viable population size

• A population is considered at risk of becoming
  extinct when its number falls below the minimum
  viable population size
• Low densities in populations can mean less
  genetic variation and less opportunities to mate

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The Allee effect

• Neanderthals may have died out when their birth
  rate became too low to offset their death rate.

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Density independent factors

• These factors limit population sizes through
  factors such as human intervention ( habitat
  destruction) or climate related events (droughts,
  floods, hurricanes)

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Limiting Factor

• Of all the resources that a population requires
  for growth, the one that is in shortest supply is
  the limiting factor
• It determines how much the population can grow.