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Population Dynamics
Population Characteristics
All populations have three main characteristics
that are used to classify the population.
1.
2.
3.
4.
Population density
Spatial Distribution
Population ranges
Growth Rate
Population Characteristics
1. Population DensityNumber of organisms per unit area
Example: pg 92
Three birds per square meter, closer to water
buffalo
Fifty meters from water buffalo, density is zero
Population Characteristics
2.
Spatial Distribution
Dispersion- the pattern of spacing a population
within a certain area.
3 types: See page 93 and draw a diagram to
show the different patterns.
a. Uniform- ex: Black bear
b. Clumped- ex: American Bison
c.
Random- ex: White-tailed Deer
Population Characteristics
3. Population Ranges
• There is no population that occupies all
habitats in the biosphere
• Population ranges can be limited by abiotic
factors such as temperature range, humidity,
annual rainfall and sunlight
• Biotic factors may be predators, competitors
and parasites
Population-Limiting Factors
Limiting factors- biotic or abiotic factors that keep
a population from increasing indefinitely.
Ex: food supply increases population increases,
food supply decreases population decreases
Two Categories of Limiting factors:
1. Density-Independent Factors
2. Density- Dependent Factors
Limiting Factors
Density-independent factors:
Any factor in the environment that does not
depend on the number of members in a
population per unit area
• Usually abiotic
• Natural phenomena (weather events)-drought,
flooding, extreme heat or cold, tornadoes,
hurricanes, and wild fires
• Human Activities- such as air, land and water
pollution
Limiting Factors
Density-dependent factors:
Any factor in the environment that depends on
the number of members in a population per
unit area
• Usually biotic factors
• Predation, disease, parasites and competition
Density-Dependent factors
Disease
1.
Outbreak of disease occurs when
population has increased and population
density is high
2.
Disease is transmitted easily when pop
density is high because contact is more frequent
3.
Disease spreads easily and quickly
Density-Dependent factors
Competition
1. Competition increases when density increases
2. Individuals must compete for resources
3. Competition can occur within a species or
between other species
4. Could result in population decrease because
of starvation or individual leaving the area
5. As population size decreases, competition
decreases
Density-Dependent factors
Parasites
1.
Similar to disease, as population density
increases parasites can negatively affect
population growth
Population Growth Rate (PGR)
Definition: Explains how fast a given population grows.
Dependent on the following factors:
1. Natality-birth rate
2. Mortality-death rate
3. Emigration-individuals moving away from
population
4. Immigration-individuals moving into a population
*******Birthrate and death rate are usually most
important when figuring out the PGR because
emigration usually equals immigration.
Exponential Growth Model
**No limits placed on growth rate by
environment
• Population grows slowly at first –lag phase
• Population rate soon begins to increase
rapidly because number of organisms that
can reproduce has increased
• J-shaped curve- Figure 7
• All populations grow exponentially until some
limiting factor slows the pop growth
Logistic Growth Model
• A S-shaped curve (figure 8)
• Occurs when the populations growth slows or
stops following exponential growth, at the
populations carrying capacity.
Carrying capacity-The maximum number of
individuals in a species that an environment can
support for the long term
• Limited by energy, water, oxygen and nutrients
available.
• The reasons why many populations stabilize