Human Population

4.2

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

2. Predation

3. Parasitism

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

in crowded populations (hi-density populations)

Predator-Prey Relationship

• Explain the diagram below:

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!

• 200 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

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.

State 4: Population decreases, birthrate lower then death rate. - Japan

Age Structure Diagrams

• Population profiles to predict future growth

STABLE

RAPID GROWTH

DECLINE

Mini-Quiz

• http://trc.ucdavis.edu/biosci10v/bis10v/media/ch28/age_structure_v2.html