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Question
With the help of a suitable diagram, describe the logistic population growth curve.
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Solution 1
Logistic growth curve of population
- Resources like food and space are not always unlimited. There may be plenty initially, but as the population density increases, competition for those resources starts, resulting in a slowdown in the rate at which the original population grows. This results in a logistic or sigmoid growth curve.
- Competition for limited resources will weed out the ‘weaker’ ones. Only the ‘fittest’ individuals will survive and reproduce.
- A given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. This limit can be called nature’s carrying capacity for that species in that habitat.
- A population growing in a habitat with limited resources initially shows a lag phase, followed by acceleration and deceleration phases, and finally an asymptote when the population density reaches the carrying capacity.
- A plot of population density in relation to time results in a sigmoid curve. This type of population growth is called Verhulst-Pearl Logistic Growth.
- Since resources for the growth of most animal populations are finite and become limiting sooner or later, the logistic growth model is considered a more realistic model.
Solution 2
In nature, no species population has unlimited resources available to allow for exponential growth. This phenomenon leads to competition between individuals for limited resources. Eventually, the ‘fittest’ individual will survive and reproduce. In nature, a given habitat has enough resources to support the maximum possible number, beyond which no further growth is likely. Let us call this limit nature’s carrying capacity (K) for the species in that habitat.
A population growing in a habitat with limited resources initially shows a lag phase. The population then experiences acceleration and deceleration, culminating in an asymptote phase. Population density, feeding capacity, and type of population growth are called Verhulst-Pearl Logistic Growth. The following equation represents it:
`(dN)/(dt) = rN ((K - N)/K) = rN (1 - N/K)`
where `(dN)/(dt)` = rate of change in population size
N = population density at time t,
r = rate of natural increase,
K = feeding capacity
Since resources for population growth are finite and become limiting, the logistic growth model is considered more realistic.
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