Population Dynamics

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Population Dynamics

• The change in the size, density, dispersion, and
  age distribution of a population in response to
  changes in environmental conditions.

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Healthy Populations

• A healthy population will grow and die at a
  steady rate unless it runs out of food or space
  or is attacked by disease or predators.

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How are populations studied?

• Introduced into study areas with abundant
  resources.
• Tracked in their natural environment.
• Population Counts Determine if a population is
  healthy and growing.
• Population Density Population per Area

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What difficulties can occur when trying to
measure a wildlife population?

• Wildlife can look alike, move, and hide resulting
  in animals being missed or counted more than once.

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So, how do you measure a population?

• Trap-Mark-Release
• Animals are trapped, marked, and released and
  then trapped a second time.
• By comparing the number of marked and unmarked
  animals in the second sampling, the population
  size can be estimated.

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So, how do you measure the size of a population?

• Sample Counts
• Used to estimate the size of a population
  scattered over a large area by sampling a smaller
  area.

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How fast do populations grow?

• Population size is affected by the birth rate,
  death rate, immigration rate, and emigration rate
  of a population.
• Birth Rate Immigration gt Death Rate
  Emigration Increase
• Birth Rate Immigration lt Death Rate
  Emigration Decrease

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Population Curves

• A population curve graphs the size of a
  population (number of individuals) on the y-axis
  over time on the x-axis.

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Population Growth

• Populations show exponential growth, not linear
  growth.
• The population growth starts out slow and then
  increases rapidly with the increasing population
  size until the carrying capacity is reached.
• Unlimited exponential growth results in an
  J-shaped population curve.

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Carrying Capacity (K)

• The largest number of individuals of one species
  that an ecosystem can support indefinitely.
• When a population reaches carrying capacity, some
  organism must either die off or find new
  resources.

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Temporary Overshoot of Carrying Capacity

• Before a population reached carrying capacity, it
  is not affected by limiting factors and can grow
  exponentially and can overshoot the carrying
  capacity.

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Temporary Overshoot of Carrying Capacity

• After the carrying capacity is exceeded, the
  resources for the population are limited and
  unless other resources are found, the population
  will suffer a crash and fall to a new lower carry
  capacity for the population.
• This results in an S-shaped population curve.

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Life-History Pattern

• An organisms reproduction pattern.
• Can vary between two extremes.
• Rapid life-history patterns
• Slow life-history patterns

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Slow Life History Patterns

• Produce a few, often large offspring, which they
  care for over a long period of time.
• Maintain stable population sizes near the
  carrying capacity.
• Populations typically follow an S-shaped curve.

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Rapid Life History Patterns

• Have a high rate of population growth (r) (Many
  offspring in a short time period.)
• Reproduce hordes of offspring early in life.
• Offspring are usually small, short-lived, and
  mature rapidly with little to no parental care.

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Rapid Life History Patterns

• Usually opportunists, reproducing rapidly when
  conditions are favorable and crashing when
  conditions are not.
• Examples insects, rodents, bacteria

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Biotic Potential

• Highest rate of reproduction under idealistic
  conditions.
• The larger the number of offspring produced by
  parent organisms, the higher the biotic potential
  of the species.

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Limiting Factors and Dispersal

• 3 Patterns of Dispersal
• Random
• Clumped (most common)
• Uniform (least common)

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Population Controls

• Density-dependent Population Controls
• Limiting Factors which become more influential as
  the population increases.
• Examples disease, competition, predators
• Density-independent Population Controls
• Effect population regardless of population size
  or dispersal.
• Examples temperature, storms, drought

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How do interactions between organisms limit
population size?

• Predator-Prey Relationships
• Predators limit the size of prey populations,
  which can then limit the size of the predator
  population.
• Competition
• Usually the most intense within the same species.
• Overcrowding and Stress

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Human Populations

• Demography
• The study of human population size, density and
  distribution, movement, and birth and death
  rates.
• Doubling Time
• The time needed for a population to double in
  size.

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Human Populations

• Age Structure
• The proportions of the population that are in
  different age levels.
• Can be used to determine stability.

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Will humans ever reach their carrying capacity?