Population Ecology

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Chapter 51

• Population Ecology

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Ecology Basics

• Terms to know
• Ecology
• Branch of biology
• Relatively new science
• Biotic factors
• Abiotic factors
• Environmental science
• ecology human interactions
• Population
• same species, same area, same time
• Population ecology
• numbers changes

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Features of populations

• Properties that individuals lack
• Population density
• Population dispersion
• Birth/death rates
• Growth rates
• Survivorship rates
• Age structure
• Properties that communities lack
• Common gene pool
• Reproductive success
• Evolution
• Economic importance (crops, forests, game
  animals)

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Population dynamics

• Density the number of individuals per unit of
  area or volume at a given period of time
• Affected by
• Habitat
• Season/Weather
• Other populations
• Limiting factors the number of individuals in a
  population is controlled by the ability of the
  environment to support it
• Density-dependent factors the effect increases
  as population density increases
• Examples
• Density-independent factors affects the size of
  a population but is not influenced by changes in
  population density typically abiotic
• Examples

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Population dynamics

• Dispersion spacing in relation to other members
  of the population
• Three basic varieties
• Clumped (aggregated distribution, patchiness)
• Individuals are concentrated in specific areas
• Reasons distribution of resources, social
  behavior of animals (herds, family groups),
  reproduction
• Advantages reduced chance of predation
• Uniform
• Individuals are fairly evenly spaced
• Reasons social behavior of animals
  (territories), high levels of competition between
  individuals
• Advantages reduced competition
• Random
• Individual spacing is unrelated to others in the
  population
• Does not occur often in nature

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Changes in population size

• Per capita per individual
• Natality average per capita birth rate (b)
• Mortality average per capita death rate (d)
• Immigration individuals entering a local
  population (i)
• Emigration individuals leaving a local
  population (e)
• Population growth rate (r)
• r (b i) (d e)
• If r positive number ? population is increasing
• If r negative number ? population is decreasing
• If r zero ? population is staying the same
• Examples

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Intrinsic rate of increase

• Maximum rate of increase when
• Conditions are ideal
• Resources are abundant
• Population density is low
• rmax
• Factors which influence this
• Age at which reproduction begins
• The fraction of the life span devoted to
  reproduction
• The number of reproductive cycles
• The number of offspring produced each cycle
• Different species have different intrinsic rates
• Small organisms have high rates (bacteria) large
  species have low rates (elephants)

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Exponential population growth

• Optimal conditions allow a constant per capita
  population growth (rmax)
• The larger the population gets, the faster it
  grows
• J shape curve
• Organisms cannot reproduce this way indefinitely
  because of increased
• competition, predation, disease, wastes

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Logistic population growth

• Population growth rate nears zero
• Occurs near the environments limits to support
  the population
• Carrying capacity (K) the largest population
  that an area can maintain indefinitely, assuming
  no changes in the environment
• S shape curve

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Density-dependent regulatory factors

• Cause an increase in death rate as the population
  increases
• Affect a larger proportion of the population, not
  just a larger number
• Can also cause a decrease in death rate as the
  population decreases
• Tend to regulate a population at a relatively
  constant size near the carrying capacity
• An example of a negative feedback system

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Cyclical population fluctuations
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Intraspecific competition

• Interference competition
• Also called contest competition
• Dominant individuals obtain resources at the
  expense of others (they interfere)
• Can cause small drops in population as the
  individuals unable to compete die
• Exploitation competition
• Also called scramble competition
• All individuals share the limited resource
• Can cause wide variation in population size

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Life history traits

• Reproductive strategies differ
• Semelparous a single, large reproductive effort
• Examples
• Iteroparous repeated reproductive cycles over
  the life span
• Examples
• Two extremes
• r-selected rapid population growth rate
• Small size, early maturity, short life span,
  large broods, little or no parental care
• Found in variable, temporary, or unstable
  environments
• K-selected keeps population at or near carrying
  capacity
• Large size, late reproduction, long life span,
  small broods, parental care of young
• Found in constant or fairly stable environments

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Survivorship curves

• Measures the probability of survival to a
  particular age
• Three basic types
• Type I young have a high chance of survival,
  probability of survival decreases with age
• humans
• Type II the probability of survival does not
  change with age
• squirrels
• Type III the probability of death is highest
  early in life
• oysters

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metapopulations

• Different populations within an ecosystem
• Due to variations of habitats
• Source habitats high quality habitats, plenty
  of resources, lots of reproductive success,
  greater population density
• Sink habitats lower-quality habitats, fewer
  resources, less reproductive success, lower
  population density
• Humans are increasing the number of
  metapopulations as they fragment ecosystems

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Human Populations

• Our population continues to increase, but this is
  due to a decrease in the death rate rather than
  an increase in the birth rate.
• This decrease is due to
• Greater food production
• Better medical care
• Improved sanitation practices
• Zero population growth (r 0)

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Human Demographics

• Highly developed countries
• Low population growth rates
• Highly industrialized
• Low infant mortality rates
• Example
• Developing countries
• Moderately developed
• Birth rates and infant mortality rates high but
  declining
• Medium industrialization
• Examples
• Less developed
• Highest birth and infant mortality rates
• Lowest amounts of industrialization
• Examples

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Age Structure Diagram

• The number and proportion of people at each age
  of a population

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Age Structure Diagrams

• Rapid growth
• Pyramid shaped as children mature, they become
  parents of the next generation and there are more
  of them than the previous group
• Slower growth or decline in population
• More tapered bases the number of
  prereproductive and reproductive ages are close
  to the same ? slower, but still positive growth
• Small bases a higher percentages of
  postreproductive ages than reproductive and
  prereproductive ages ? negative growth (decline)

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Environmental degradation

• People overpopulation.
• Developing countries
• Examples
• Consumption overpopulation
• Developed countries
• Examples