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Chapter 5: Populations
5-1: How Populations Grow
Characteristics of Population
1. Geographic
Distribution: “range”,
area inhabited by a
population
2. Density: # of
individuals per unit of
area
3. Growth Rate:
Increase, Decrease, or
Stay the Same
Population Growth
• 3 Factors that affect population growth
– # of births (birth rate)
– # of deaths (death rate)
– # entering and # leaving
• Immigration: movement of individuals into an area
(growth)
• Emigration: movement of individuals out of an area
(decrease)
Exponential Growth
• Exponential Growth: individuals
reproduce at a constant rate
– Ideal conditions with unlimited
resources are necessary for
exponential growth.
Ex: One bacteria cell reproduces
every 20 minutes
How many bacteria 20 min later?
How many another 20 min later?
How many after another 20 min?
How many after one day?
Logistic Growth
• Logistic Growth: when
population growth slows or
stops (due to decreased
availability of resources)
• Carrying Capacity: The
largest number of
individuals that an
environment can support
5-2: Limits to Growth
Limiting Factors
•
Limiting Factor: Causes population growth
to decrease
1.
2.
3.
4.
5.
Competition
Predation
Parasitism/Disease
Extreme Climates
Human Disturbances
Density Dependent Factors
• Density Dependent Limiting Factors – depends on
population size and density
• Factors act most strongly when population is large
and dense
– Ex: Competition: compete for resource
– Ex: Predation: one catches & feeds on another;
population rise and fall in tandem
– Ex: Parasitism: organisms take nourishment at
expense of host, weakening or killing host.
Density-Independent Factors
• Density –Independent Limiting Factors:
affect all populations, regardless of size
– EX: weather, natural disaster, seasons, and
humans
5-3 Human Population Growth
Human Population Growth
• Size of human population increased with
time
• Started slow, grew rapidly due to:
–
–
–
–
Agriculture
Industry
Medicine
Sanitation
Patterns of Population Growth
• Demography: scientific study of human
populations
• “The Demographic Transition” – a dramatic
change in birth and death rates
–
–
–
–
In developing countries birth and death rates are high
As country develops, death rate is lowered
Population increases and birth rate is lowered
U.S, Japan, and much of Europe have completed the
transition
Age Structure
• Age Structure Diagram: graph the numbers of
people in different age groups in a population
– Used to predict future population growth
Future Population Growth
• Estimated human population in 2025?
– 7.8 Billion People
• Estimate human population in 2050?
– 9 Billion People
• If the human population growth
doesn’t slow down it could seriously
damage the environment and global
economy.