Population dynamics
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Population Dynamics. Population Characteristics. All populations have three main characteristics that are used to classify the population. Population density Spatial Distribution Population ranges Growth Rate. Population Characteristics. 1. Population Density-

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Population Dynamics

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Population dynamics

Population Dynamics


Population characteristics

Population Characteristics

All populations have three main characteristics that are used to classify the population.

  • Population density

  • Spatial Distribution

  • Population ranges

  • Growth Rate


Population characteristics1

Population Characteristics

1. Population Density-

Number 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 characteristics2

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 characteristics3

Population Characteristics

  • 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

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:

  • Density-Independent Factors

    2. Density- Dependent Factors


Limiting 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 factors1

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

Density-Dependent factorsDisease

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

Density-Dependent factorsCompetition

  • Competition increases when density increases

  • Individuals must compete for resources

  • Competition can occur within a species or between other species

  • Could result in population decrease because of starvation or individual leaving the area

  • As population size decreases, competition decreases


Density dependent factors parasites

Density-Dependent factorsParasites

1.Similar to disease, as population density increases parasites can negatively affect population growth


Population growth rate pgr

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

  • Emigration-individuals moving away from population

  • 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

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

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


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