This lecture introduces the concepts for the population growth lab assignment.

1. Lab 6
Population Growth Model
Dr. Davenport

2. Objectives
• To understand the population growth models
under different conditions.
– Geometric population growth
– Exponential population growth
– Logistic population growth

3. Geometric Growth
• When generations do not overlap and there is no
resource limitation, growth of a population can be
modeled geometric population growth
• (such as annual plant…)
Nt = No  t
– Nt = Number of individuals at time t.
– No = Initial number of individuals.
–  = Geometric rate of increase.
– t = Number of time intervals or generations.
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5. Exponential Growth
• When a population is a continuous population (does have
generation overlap), and in an unlimited environment this
population growth can be modeled as exponential population
growth
dN/dt = rN
• dN/dt = the rate of population growth.
• r= per capita rate of increase.
• N = population size
• It is appropriate to model the over-lapping generation,
continuous population under unlimited environments.
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8. • However, the exponential growth cannot
continue indefinitely.
• The limited environmental resources will
slowdown the population growth.
• The effect of the environment on population
growth is reflected in the shapes of
population growth curves.
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9. Why does population growth
slowdown????
• limited environmental resources will
slowdown the population growth. ---- but
why????
• When environmental resources become
limited, the individuals in the population will
compete with each other for limited resource.
This competition will slowdown the
population growth.

10. Logistic Population Growth
• As resources are depleted, population growth rate
slows and eventually stops: logistic population
growth.
dN/dt = rN(1-N/K)
– Carrying capacity (K) is the number of individuals of a
population the environment can support.
– Finite amount of resources can only support a finite
number of individuals.
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11. Logistic Population Growth
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Sigmoid (S-shaped) population growth curve.

12. • So, dN/dt = rN(1-N/K)
• Represent the effects of competition on
population growth.
• Which term in the model describe the
intraspecific competition???
• N/K