Chapter 5: Populations

Introduction phenomenon: How do scientists determine the size of a population?


Why do we need to know a population's size?



5-1 How Populations Grow

Geographic distribution – the area a pop lives(range)

Population Density – the number of individuals in an area

Population Growth

Number of births

Number of deaths

Emigration (out) & Immigration (in)

For example, In Springfield, 45 babies are born in the year 2008. 15 people died that same year. What is the growth rate for the city?

Positive Growth rate = population increase
Negative Growth rate = decrease
Exponential Growth –reproduce at a constant rate. Occurs under ideal conditions (no limits)

J-shape curve

Logistic Growth – resources become less available, growth slows or stops

S-shape curve

Carrying Capacity – the number an environment can support


5-2 Limits to Growth

Limiting Factor – causes population growth to decrease

Density-Dependent Factors –depends on population size



parasitism and disease

Density-Independent Factors – does not depend on population size

Unusual weather

Natural disasters

Some human activities

Predator Prey Relationships

As prey population goes up, so does predator population. What happens when the prey population goes down?

predator graph

Demography: The study of human populations

Demographic Transition – a dramatic change in birth and death rates

Age Structure Diagrams can be used to evaluate populations