Limits to GrowthHuman Population Growth

5-2 and 5-3

Population Growth Is Limited

• Limiting Factor: factor that causes population growth to decrease

• 2 kinds of limiting factors1. Density-Dependent Factors: depends

on populations size2. Density-Independent Factors: affect all

populations in similar ways, regardless of size

Density Dependent Limiting Factors

• Density: the number of organisms per unit area

1. Competition-

(food, shelter, mate)

2. Predation

3. Parasitism

4. Disease• Be able to explain why these factors are present

in crowded populations (hi-density populations)

Predator-Prey Relationship

Density Independent Limiting Factor

• Affects all populations in the same way, regardless of size

1. Unusual weather

2. Natural disasters

3. Human activities

4. Seasonal cycles

• Can you give an example for each listed above?

Human Populations

• In history, human population remained constant (no growth or decline)

• High birth rate and high death rate

Population Growth Goes Exponential!

• 500 years ago, human population began to explode…– Agriculture– Industry– Medicine– Improved Sanitation– Healthcare

• This drastically reduced the death rate, but didn’t change birth rate

Modeling Growth

• Demography: Scientific study of human populations

• Observation: US, Japan, Europe growth slows

• Experiment: collect data (US Census)• Model: “Demographic Transition”

Hypothesis

Comment on the Graph Below

Demographic Transition

:A dramatic change in birth rate and death rate• Stage 1: High birthrate and high death rate

– Most countries in early history• Stage 2: High birthrate and low death rate

– US (1790-1910), developing countries• Stage 3: Low birthrate and low death rate

– US (now), Europe, and Japan

Age Structure Diagrams• Population profiles to predict future growth

STABLE

RAPID GROWTH

DECLINE

Growing Populations

Not Growing

Check Yourself

• What type of growth does each graph show?

Explain This Age Structure Diagram