Population ecology
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Population Ecology. Warm-up Question : If humans have no natural predators, how is our population controlled? Provide examples. . Key Terms. Demography- study of human populations Density- number of individuals per unit area

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Population ecology

Population Ecology

Warm-up Question: If humans have no natural predators, how is our population controlled? Provide examples.

Key terms
Key Terms

  • Demography- study of human populations

  • Density- number of individuals per unit area

  • Dispersion- relative arrangement of individuals within a given amount of space



Growth rates
Growth Rates

  • Growth Rate: change in population over time

    • Positive (+): birth rate > death rate

    • Zero (0): birth rate = death rate

    • Negative (-) = birth rate < death rate

  • Fertility Rate: The average number of offspring a female has in its lifetime

  • Replacement Rate: each mating couple has two offspring that survive to reproduce, replacing parents (fertility rate = 2.1)

Reproductive potential
Reproductive Potential

  • Maximum number of offspring each member of a population can produce

  • Increases when members reproduce often and earlier in their reproductive life

  • Generation time- time it takes for an average member of a population to reproduce.

    • Human Generation time: 20 years

    • E.Coli Generation time: 17 minutes

Exponential growth
Exponential Growth

  • Increase in population size due to a constant growth rate

  • Unlimited resources

  • Ideal conditions

  • “J” curve

Logistic growth
Logistic Growth

  • Population growth slows or stops following a period of exponential growth

  • Birth rate decreases, Death rate increases OR Both

  • “S curve”

Carrying capacity k
Carrying Capacity (K)

  • The maximum amount of individuals an environment can support

  • What happens to growth rate as it approaches K?

Reaching carrying capacity
Reaching Carrying Capacity


Logistic growth overshoot
Logistic Growth- “Overshoot”

Population grows beyond carrying capacity and collapses

Carrying Capacity is often diminished due to overshoot


Limiting factors
Limiting Factors

Pair and Share (2 min):

  • What factors would cause a population’s size to increase?

  • What factors would cause a population’s size to decrease?

Limiting factors1
Limiting Factors

  • Food

  • Water

  • Sunlight (producers)

  • Space

  • Disease

  • Competition

Limiting populations
Limiting Populations



Size of population does not matter;

Deaths occur independently of population density

Ex: natural disasters

  • Deaths occur more quickly in a more crowded environment

  • Limited resources

  • Disease

Human carrying capacity
Human Carrying Capacity?

  • Current human population: 7.12 billion people

  • Ranges estimated from 4-16 billion people

  • Hard to estimate how many people this world can hold

    • Technological innovations

    • Medical breakthroughs

  • http://www.census.gov/popclock/

What sparked our growth
What sparked our growth?

  • Industrial Revolution (~1750)

  • Modern medicine (20th century)

    • Death rates DROPPED due to better care

  • Agricultural Advances

  • Transportation Advances

Human population growth
Human Population Growth

Source: U.S. Census Bureau- World POPclock Projection

What takes us out
What takes us out?

Humans are at the top of any food web resulting in no natural predators to keep our populations in check…

  • What are the limiting factors of the human population?

  • How are we different than other species in regards to population control?

What s our limiting factor
What’s our limiting factor?

  • Disease: Bubonic Plague, AIDS, Flu, Malaria

  • Access to food

  • Access to clean water

  • Competition (a.k.a. War)