Ecology of Populations

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Ecology of Populations
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Outline

• Scope of Ecology
• Population Density and Distribution
• Population Growth Models
• Survivorship Curves
• Age Distributions
• Regulation of Population Size
• Life History Patterns
• Human Population Growth
• Environmental Impact

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Scope of Ecology

• Ecology - Study of the interactions of organisms
  with other organisms and the physical
  environment.
• Habitat - Place where an organism lives.
• Population - All the organisms within an area
  belonging to the same species.
• Community - All various populations interacting
  at same locale.
• Ecosystem - Community of populations.

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Ecological Levels
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Density and Distribution of Populations

• Population Density - Number of individuals per
  unit area or volume.
• Population Distribution - Pattern of dispersal of
  individuals within the area of interest.
• Ecologists want to analyze and discover what
  causes the spatial and temporal patchiness of
  organisms.
• Limiting Factors are factors that particularly
  determine whether an organism lives in an area.

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Uniform Distribution
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Random Distribution
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Clumped Distribution
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Characteristics of Populations

• Intrinsic Rate of Natural Increase (r)
• If immigration () and emigration (-) cancel each
  other out, then population growth can simply be
  modeled by birth rate minus the death rate.

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Population Growth Models

• Exponential Growth
• Number of individuals added each generation
  increases as the total number of females
  increases.
• Biotic Potential - Maximum population growth that
  can possibly occur under ideal circumstances.
• Environmental Resistance - All environmental
  conditions that prevent populations from
  achieving biotic potential.

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Exponential Growth Curve
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Exponential Growth Equation
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Logistic Growth

• Logistic growth occurs when environmental
  resistance comes into play and retards
  exponential growth.
• Living populations must eventually come under the
  control of environmental resistance.

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Logistic Growth
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Logistic Growth
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Carrying Capacity

• Carrying Capacity is the maximum number of
  individuals of a given species the environment
  can support.
• The closer the population to the carrying
  capacity, the greater the environmental
  resistance.
• Biotic potential is having full effect and
  birthrate is a maximum during exponential growth.

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Mortality Patterns

• A cohort is composed of all the members of a
  population born at the same time.
• Survivorship is the probability of newborn
  individuals of a cohort surviving to particular
  ages.
• Survivorship Curves

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Survivorship Curves
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Survivorship Curves
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Age Distributions

• Populations differ according to what proportion
  of the population falls in each age category.
• At least three structures possible.
• Increasing
• Stable
• Decreasing

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U.S. Age Distributions
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Regulation of Population Size

• Density - Dependent Factors
• Number of organisms present influences the effect
  of the factor.
• Competition
• Predation
• Density - Independent Factors
• Number of organisms present does not influence
  the effect of the factor.
• Natural Disasters

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Life History Patterns

• r - Strategists (Opportunistic)
• Produce large numbers of offspring.
• Small body size.
• Early maturity
• No parental care.
• Density independent controls.
• Good dispersers and colonizers.

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Life History Patterns

• k - Strategists (Equilibrium)
• Produce small numbers of offspring.
• Large body size.
• Late maturity
• Significant parental care.
• Density dependent controls.
• Specialists

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Human Population Growth

• Human population has an exponential growth
  pattern.
• Doubling time currently estimated at 53 years.
• Population Size
• 1800 1 Billion
• 1930 2 Billion
• 1960 3 Billion
• 2000 6 Billion

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World Population Growth
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Country Development

• More-Developed Countries (MDCs)
• Slow population growth.
• High standard of living.
• Completed Demographic Transition.
• North America and Europe
• Less-Developed Countries (LDCs)
• Rapid population growth.
• Low standard of living.
• Latin America
• Africa and Asia

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Age Distributions

• Age Structure Diagrams divide populations into
  three age groups.
• Pre-Reproductive
• Reproductive
• Post-Reproductive

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More-Developed Countries
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Less-Developed Countries
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Environmental Impact

• Environmental impact of a population is measured
  in terms of
• Population Size
• Resource Consumption Per Capita
• Resultant Pollution

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Environmental Impact
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Review

• Scope of Ecology
• Population Density and Distribution
• Population Growth Models
• Survivorship Curves
• Age Distributions
• Regulation of Population Size
• Life History Patterns
• Human Population Growth
• Environmental Impact

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