Lab 6 Population Growth Model

Dr. Davenport

Objectives

• To understand the population growth models under different conditions.

– Geometric population growth– Exponential population growth– Logistic population growth

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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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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• 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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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.

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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Logistic Population Growth

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Sigmoid (S-shaped) population growth curve.

• 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