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Population Characteristics
• Geographic Distribution/Range- describes
area inhabited by population of organisms
• Population Density- number of individuals per
unit area; varies depending on species and its
• Growth rate- change in number of
organisms/size of population over time
• Age structure diagrams
Factors affecting
Population size
Number of births
Number of deaths
Emigration-# leaving population
Immigration-# entering population
Growth Charts
• Direct/Linear- rate of population growth
constant over time
• Exponential- (J-shape curve)- Rate of growth
increases with time (note: ideal
conditions/unlimited resources)
• Logistic-(S-shaped curve)- realistic way of
expressing growth-limiting factors
– Carrying capacity- largest number of
organisms a given environment can
Limits to growth
• Limiting factors- factors causing population growth to
– Density-Dependent factors- affect population more
strongly as population increases in size
– Examples: Competition, Predation, Disease,
– Density-Independent- same impact no matter
population size
– Examples: Unusual weather, Natural disaster,
Seasonal cycles, Human activities
Age Structure Diagrams
• Deals with human population growth
• Size of human population tends to increase with
time; Exponential growth
• Demography- scientific study of human population;
how human population changes with time
• Birth rates, Death rates and age structure diagrams
help predict why some countries have high growth
rates and other countries grow more slowly
Age Structure Diagrams
• Demographic transition- dramatic
changes in birth/death rates
• Countries modernize and advances in
nutrition, sanitation and medicine allow
more children to survive to adulthood
• First, graph shows a lowering of the
death rate (begin transition)
Age Structure Diagrams
• Next, birthrates remain high (B>D) and
population grows exponentially
• Countries continue to modernize,
families begin to have fewer children
and birthrate begins to
decrease/population begins to slow
down and population growth stops (end
of transition)
Age Structure Diagrams
• Predict future growth
• How many people of different ages
(and genders) make up population
• U.S.- equal number of people across
ages/gender; steady growth/slow
• Nigeria- far higher number of young vs.
old people; foresee large population
growth/double over next 30 years