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Are we over carrying capacity?. Population density/consumption patterns. Quality of life issues. Impact on landscapes & resources Lake Chad. What is “overpopulation”?. how does it occur?. Outline. Basic Dynamics of Population Growth Exponential vs. Arithmetic Growth

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Are we over carrying capacity?

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Are we over carrying capacity

Are we over carrying capacity?

Population density consumption patterns

Population density/consumption patterns

Quality of life issues

Quality of life issues

Impact on landscapes resources lake chad

Impact on landscapes & resourcesLake Chad

What is overpopulation

What is “overpopulation”?

how does it occur?



  • Basic Dynamics of Population Growth

    • Exponential vs. Arithmetic Growth

    • Malthusian vs. Logistic Growth

  • Complex Patterns of Population Change

  • Regulating Population Growth

    • Density Dependence vs. Independence

  • How do we apply possibilities to a specific case?

Dynamics of population growth


  • Exponential Growth - Growth at a constant rate of increase per unit time (Geometric)

  • Arithmetic Growth - Growth at a constant amount per unit time (independent of base)

Exponential growth and doubling times

Exponential Growth and Doubling Times

  • Number of individuals added to a population at the beginning of exponential growth is relatively small.

  • But numbers increase quickly as the reproductive base of the population grows.

    • J curve is the result of exponential growth

  • Doubling Time of a population:

    • 70/annual percentage growth rate.

Irruptive growth

Irruptive Growth

  • Malthusian Growth (Irruptive) - Population explosions followed by population crashes.

    • Malthus concluded human populations tend to grow exponentially until they exhaust their resources and then crash.

    • Non-human examples are common, but may be influenced by predators or parasites, not just resources

Irruptive population examples

Irruptive population examples

Malthusian strategies

Short life

Rapid growth

Early maturity

Many small offspring

Little parental care

Little investment in individual offspring.

Adapted to unstable environment.

Pioneers, colonizers

Niche generalists


Regulated mainly by extrinsic factors.

Low trophic level

Malthusian Strategies

Biotic potential and carrying capacity

Biotic Potential and Carrying Capacity

  • Biotic Potential - Maximum reproductive rate of an organism (births minus deaths in optimal conditions).

  • Carrying Capacity - Maximum number of individuals of any species that can be indefinitely supported

Growth to a stable population

Growth to a Stable Population

  • Logistic Growth - Growth rates regulated by internal and external factors until coming into equilibrium with environmental resources.

    • Growth rate slows as population approaches carrying capacity.

    • S curve

  • Environmental Resistance - Any environmental factor that reduces population growth.

Logistic strategies

Long life

Slower growth

Late maturity

Fewer large offspring

High parental care and protection.

High investment in individual offspring.

Adapted to stable environment.

Later stages of succession.

Niche specialists


Regulated mainly by intrinsic factors.

High trophic level

Logistic Strategies

Population oscillations around carrying capacity

Population Oscillations around Carrying Capacity

  • Overshoot - Measure of extent to which population exceeds carrying capacity of its environment.

  • Dieback - Negative growth curve.

    • Severity of dieback generally related to the extent of overshoot.

Factors that add to populations


  • Natality - Production of new individuals .

    • Fecundity - Physical ability to reproduce.

    • Fertility - Measure of actual number of offspring produced.

  • Immigration - Organisms introduced into new ecosystems.

Losses mortality and emigration

LOSSES: Mortality and Emigration

  • Mortality - Death Rate.

    • Survivorship - Percentage of cohort surviving to a certain age.

    • Life expectancy - Probable number of years of survival for an individual of a given age.

      • Increases as humans age.

    • Life Span - Longest period of life reached by a given type of organism.

  • Emigration - Movement of individuals out of a population.

Factors that regulate additions and losses


  • Intrinsic factors - Operate within or between individual organisms in the same species.

  • Extrinsic factors - Imposed from outside the population.

  • Biotic factors - Caused by living organisms.

  • Abiotic factors - Caused by non-living environmental components.

Density independent regulatory factors

Density-Independent Regulatory Factors

  • Constant proportion of the population is affected regardless of population density.

  • Tend to be abiotic components affecting mortality.

  • The risk (per individual) is unrelated to the density of individuals (e.g, tsunami).

Density dependent factors

Density-Dependent Factors

  • Intensity changes as the population density changes.

  • Tend to reduce population size by decreasing natality or increasing mortality.

    • Interspecific Interactions

      • Predator-Prey oscillations

    • Intraspecific Interactions

      • Territoriality

    • Stress and Crowding

      • Stress-related diseases

Are we over carrying capacity

Given a long list of possible factors promoting growth, for a specific case, what leads to overpopulation or extinction?

  • Identify most likely influences

    • (create a simplified “model”)

  • Test the predictions of the model

  • Example, what are the most likely influences on population levels of White-tailed Deer in Knox County?

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