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Population growth
Appears in
Concepts tested here
- Logistic growth equation
- Population density change
All Questions
2013 NEET 1 question
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A biologist studied the population of rats in a barn. He found that the average natality was 250, average mortality 240, immigration 20 and emigration 30. The net increase in population is:Net increase = (natality + immigration) − (mortality + emigration) = (250 + 20) − (240 + 30) = 0
2011 AIPMT-MAINS 1 question
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The logistic population growth is expressed by the equationWhen resources are unlimited, a population grows exponentially: $\frac{dN}{dt} = rN$ (J-shaped curve).
In nature resources are limited, and a habitat can support only a maximum number of individuals, the carrying capacity K.
Such a population shows a lag phase, then acceleration, deceleration and finally an asymptote when N reaches K (sigmoid curve). This is Verhulst–Pearl logistic growth.
It is described by $\frac{dN}{dt} = rN\left(\frac{K - N}{K}\right)$, where N is the population density at time t and r is the intrinsic rate of natural increase.
The factor $\frac{K - N}{K}$ is the environmental resistance term; as N approaches K it becomes zero and growth stops.
Hence the logistic equation is $dN/dt = rN\left(\frac{K - N}{K}\right)$.