Population Dynamics

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Population Dynamics

• Text 8.1

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population

• Number of members of a single species in a
  particular area

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3 characteristics of all populations

• Density
• The number of organisms of the same species per
  unit area (25 people per classroom)
• Dispersion
• The pattern of population distribution
• Ranges
• Limited by biotic and abiotic factors

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Population density

• The number of organisms per unit area.
• High population density crowded
• So cities have
• High people population density, but low
• Trees and other organisms that got displaced

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Dispersion

• often dictated by availability of food.
• Uniform dispersion
• Evenly spaced
• Territorial animals protect their hunting
  grounds, creating this.
• Clumped dispersion
• Social animals that live in herds or colonies
• Examples?
• Buffalo, ants, bees, wildebeast, schools of fish

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Dispersion continued

• Random dispersion
• Neither territorial nor colonizing
• Unpredictable
• Examples
• Deer, many birds (except when they group together
  to migrate)

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Range

• Can be very small, like
• limited to an island
• Or vast, like
• almost everywhere on the planet
• Mosquitos
• Range is determined by both biotic and abiotic
  factors

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Population Limiting Factors

• Density independent factors
• Factors that do/dont (pick one) depend on the
  population density
• Dont
• So abiotic factors, such as weather events,
  including
• Drought, flood, fire, tornados

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Population Limiting Factors

• Density dependent factors
• Biotic factors limit the population
• Amount of food (plants or prey)
• Amount of predators
• Amount of competition for same resource
• The higher the population, the more competition
• Disease (higher rate with higher population
  density)

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Population growth rate

• Emigration
• Leaving the population
• Immigration
• Coming in to the population
• Pop. by
• emigration and mortality (death)
• Pop. by
• Immigration and birth

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Population growth rate

• If population increase and decrease are equal,
  then population growth rate is
• Zero
• If immigration and birth exceed (are greater
  than, gt) emigration and death, then population
  growth rate is
• Positive
• What are the factors that make population growth
  negative?
• More deaths and emigration than births and
  immigration.

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Growth models

• Exponential and logistical growth models
• Exponential
• All pops. would do this if not limited
• Happens when a population arrives in a new area
  with no competition and plenty of food

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Exponential growth
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Exponential growth
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Growth Models

• Logistical
• S curve
• Exponential growth until limiting factors bring
  under control
• Then stable

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Carrying capacity

• The maximum number of individuals of a species an
  area can support over the long term
• Limited by biotic (predation, food availability)
  and abiotic (land space for nesting, etc) factors

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Reproductive patterns

• r-strategists and k-strategists
• r-strategists
• Produce many offspring
• Dont spend much energy caring for young
• most offspring die, best adapted survive
• Typical for fluctuating environment
• Examples
• Dandelions,
• sponges,
• sea turtles

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Reproductive patterns

• k-strategist
• Tend to be larger animals
• Produce few offspring
• Care for their young
• Most offspring survive
• Environmental conditions generally stable
• Controlled by density dependent factors
• Examples
• Most mammals, large birds,

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R-strategist or k-strategist?
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R-strategist or k-strategist?

• You Think of one and share with neighbor