Population EcologyThe factors and interactions that affect

population size

How do we study populations? 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

Population Density of U.S.

Dispersion• There are 3 types:

Dispersion

How do we study populations?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 their parents.

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

Population Growth Curves

Exponential Growth

• Increase in population size due to a constant growth rate

• Unlimited resources

• Ideal conditions

• “J” curve

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)

• The maximum amount of individuals an environment can support

• What happens to growth rate as it approaches K?

Reaching Carrying Capacity

www.algebralab.org

Logistic Growth- “Overshoot”

rewild.info 

Carrying Capacity is

often diminished

due to overshoot

Population grows beyond carrying

capacity and collapses

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 Factors

• Food

• Water

• Sunlight (producers)

• Space

• Disease

• Competition

• Predation

Limiting Populations

Density-Dependent

• Deaths occur more quickly in a more crowded environment

• Limited resources

• Disease

Density-Independent

• Size of population does not matter;

• Deaths occur independently of population density

• Ex: natural disasters

If humans have no natural predators,

how is our population

controlled?

Human Carrying Capacity?

• Current human population: approx 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 caused this

rapid 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

Population (in billions) 1 2 3 4 5 6 7 8 9

Year 1804

1927

1960

1974

1987

1999

2012 2027 2046

Years elapsed between milestones

-- 123 33 14 13 12 13 16 19

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

What takes us out?

Pair and Share (2 min):

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

1. What are the limiting factors of the human population?

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

What’s our limiting factor?

• Disease: Bubonic Plague, AIDS, Flu, Malaria

• Access to food

• Access to clean water

• Competition (a.k.a. War)

Event Casualties

American War Deaths, all-time

600,000

India Famine (1769-70) 3,000,000

AIDS deaths in 2011 1,700,000

Influenza Epidemic (1918) 21,000,000

Indonesian Tsunami/Earthquake

(2004)

230,000

Bubonic Plague (1347-51) 75,000,000