Download Chapter 5 Notes

Chapter 5
5-1 How Populations Grow
Characteristics of Populations
 Geographic Distribution – the area inhabited by a population
 Population Density – number of individuals per unit area
 Growth Rate – an increase or decrease of the number of individuals in a population
over time
Population Growth/Decline
 A population can grow when its birthrate is greater than its death rate
 Immigration – movement of individuals into an area
 Populations can increase
 Animals maybe searching for mates or food
 Emigration – movement of individuals out of an area
 Populations can decrease
 Animals leave to find mates or food
 Exponential Growth
 Under ideal conditions with unlimited resources a population will grow
exponentially resulting in a population explosion
 Exponential growth is characterized by a J-shaped curve
 In nature exponential growth does not continue in a population for very long
 As resources become less available, the growth of a population slows or stops
 Logistic Growth
 Occurs when a population’s growth slows or stops following a period of
exponential growth
 Logistic growth is characterized by a S-shaped curve
 What prevents the world from being overrun with all kinds of living things?
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 Carrying Capacity – the number of organisms of one species that an environment
can support
 When a population reaches the carrying capacity of its environment, its growth
levels off
5-2 Limits to Growth
Limiting Factors
 Limiting Factor – a factor that causes population growth to decrease
 Density-Dependent Factors – a limiting factor that depends on population size
 These factors operate most strongly when a population is large and dense
 As populations increase so do these factors
 Example: competition, predation, parasitism, disease
 Density-Independent Factor – a limiting factor that affects all populations regardless
of the population size
 Example: natural disasters, storms, floods, drought, pollution
5-3 Human Population Growth
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Demography – the study of human population growth
For most of human existence, the population grew slowly
Limiting factors kept population sizes low
About 500 years age, the human population began growing more rapidly
Life was made easier and safer by advances in agriculture and industry
Death rates were dramatically reduced due to improved sanitation, medicine, and
healthcare, while birthrates remained high
With these advances, the human population experienced exponential growth
Age Structure
 Age-Structure Diagrams – show the population of a country broken down by
gender and age group
 Population growth depends, in part, on how many people of different ages make
up a given population
 Demographers can predict future growth using age-structure diagrams
How can you tell if a population is growing?
 If the birth rate is more than the death rate
Does it make a difference to population growth if the largest proportion of the
population is in one age group?
 If a large percent of the population is teenagers and children there is rapid growth
 If the percent of people in each category is equal the population is stable
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