Download Population Dynamics – Growth Rates

Population Dynamics –
Growth Rates
Chapter 4
Learning Targets
 I can…
1.
2.
3.
Explain the concept of carrying capacity
Model how limiting factors and organism
interactions affect carrying capacity
Describe the growth of populations using
logistic and exponential growth models
Limiting Factors
 All species have limiting factors

Limiting Factors: an abiotic or biotic factor
that restricts the number, distribution, or
reproduction of a population of organisms

Examples:
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Food
Shelter
Space
Water
Limiting Factors
 Density - Independent Factors: any factor in
an organisms’ environment that does not
depend on the number of individuals in the
population


Usually abiotic and include natural
phenomena such as weather events
Ex: rain, drought, tornado, fire, etc.
Limiting Factors
 Density-Dependent Factors: any factor in the
environment that depend on the number of
individuals in a population
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Often biotic factors
Ex: predation, disease, parasites, and
competition
Carrying Capacity
 Carrying Capacity – the maximum number
of individuals an environment can support
long term

The carrying capacity of organisms is limited
by the amount of resources available to the
population
Population Growth Rates

Population Growth Rate – explains how fast a
given population grows

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Natality – birth rate (# of births each year)
Mortality – death rate (# of deaths each year)
Population Growth Rates
 Population growth rates include info about
individuals who enter or leave

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Emigration – describes the number of
individuals moving away from a population
Immigration – describes the number of
individuals moving into a population
Population Growth Rates
 In order to notice trends of population
growth over multiple years, ecologists look at
mathematical models
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Exponential Growth Model
Logistic Growth Model
Exponential Growth Model
 Exponential Growth Model – occurs when
the growth rate is proportional to the size of
the population

All populations grow exponentially until
some limiting factors slows the population’s
growth
Exponential Growth Model
 The graph begins with a lag period

Reproduction of the population occurs slowly
 The rate of population growth increases
rapidly because the total number of
organisms that can reproduce has increased

Called Exponential growth period
 The graph is recognizable by the J-shape it
creates
Logistic Growth Model
 Logistic Growth occurs when the
population’s growth slows or stops following
exponential growth

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Occurs after reaching the carrying capacity
Many populations grow more like this model
than the exponential model
Number of births is less than the number of
deaths
Recognized by the S-shape on graph
Logistic Growth Model