Population Ecology Chapter 4

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Population Ecology Chapter 4
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Population

• An interacting group of individuals of a species
  that use common resources and are regulated by
  the same natural phenomena, such as temperature,
  water and food supply, and predation
• Population density-the number of individuals of a
  species per unit area or volume

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Key Concepts

• Factors affecting population size

• Species reproductive patterns

• Species survivorship patterns

• Conservation biology and human impacts on
  ecosystems

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Spatial Distribution
Dispersion the pattern of spacing of a
population within an area
Population ranges- not all species occupy all
habitats in the biosphere limited and vast
ranges
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Dispersion Patterns
Random occurs when Individuals are spaced, in a
patternless, unpre- dictable way. Dandelions And
white-tailed deer are examples.
Uniform is even pattern of Dispersion that of
results Interactions among Individuals of a
population Creosote bush and black Bears are
examples
Clumped is when individuals are aggregated into
patches, is the most common in nature. Elephants
and the American Bison are clumped in
groups herds.
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Density Independent Factors Limit Population
Growth

• Density Independent density of the population
  doesnt matter, the population will be affected

• Natural disasters (climate, weather)
• environmental factors (fire, floods, storms)
  and
• habitat disruption by human activity

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Density Dependent Factors Limit Population Growth

• Density Dependent when population-limiting
• factors depend on the density of the
  population

• Competition for resources

• Predation

• Parasitism

• Disease

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What Limits a Population?

• Birth

• Death

• Emigration

• Immigration

? Population (Birth Immigration) - (Deaths
Emigration)
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Growth Models

• Exponential Growth Model -gives an idealized
  picture of the unregulated growth of a population
• Equation is G rN describes the J-shaped curve,
  which is typical of exponential growth Ggrowth,
  rintrinsic rate of increase, Npopulation size
• The bigger the value of N, the faster the
  population increases
• The lower part of the J results from the
  relatively slow growth when the population is
  small
• The steep, upper part of the J results from N
  being large

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Growth Models

• Logistic Growth Model-a description of idealized
  population growth that is slowed by limiting
  factors results in a sigmoidal or S shaped
  curve
• Describes the effect of population-limiting
  factors as well as population growth
• Equation is more complicated than exponential
  (K-N)/K K is for carrying capacity
• Carrying Capacity is the number of individuals in
  a population that the environment can maintain
  carry without a net increase or decrease.

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Population Growth Curves
Logistic - s curve, exponential growth,
environmental effects, then leveling
Exponential - J curve, starts slow then fast
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What affects K? (Carrying Capacity

• competition

• immigration emigration

• natural human caused catastrophes

• seasonal fluctuations affect food, water,
  shelter

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Reproductive Patterns

• Depends on several factors
• Species vary in the number of births per
  reproduction cycle, in the age reproduction
  begins, and in the life span of the organism
• R-strategy is an adaptation for living in an
  environment where fluctuation of biotic and
  abiotic factors occur (availability of food or
  changes in temperature)
• R-strategist is usually a small organism such as
  a fruit fly, mouse or locust. Generally have
  short life spans and produce many offspring.
• Expend little or no energy in raising their young
  to adulthood
• Controlled by density-independent factors
• Do not maintain a population near its carrying
  capacity

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Reproductive Patterns

• K-strategy or carrying capacity is an adaptation
  for living in predictable environments
• K-strategist is generally a larger organism with
  a long life span
• Produces few offspring whose population reaches
  carrying capacity
• Have a better chance of survival because energy,
  resources and time is invested in caring for the
  young
• Controlled by density-dependent factors

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Survivorship Curves

• Type 1 survivorship curve ex. Whales, elephants,
  humans
• High survival rates until old age.
• Example

humans
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Survivorship Curves

• Type 2 survivorship curve mortality constant
  over the life span ex. Hydras, squirrels
• Intermediate between the extremes.
• Example

squirrel
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Survivorship Curves

• Type 3 survivorship curve
• High mortality (death) rates as larvae/very
  young but decreased mortality at later ages.
• Example

oysters frogs insects
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Survivorship Curves
Fig. 9.11, p. 206
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Trends in Human Population Growth

• Demographic transition is a change in a
  population from high birth and death rates to low
  birth and death rates
• If (Birth Immigration) (Deaths Emigration)
• then its called
• ZERO POPULATION GROWTH

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Age Structure Diagrams

• Gives the proportion of individuals in different
  age groups