$(b)$

Logistic model shows that

As population increases the competition goes on increasing.

Logistic Growth Model No population can continue to grow exponentially, as the resource availability become limiting at certain point of time. Logistic growth model have fixed carrying capacity

It is described by the equation $\frac{d N}{d t}=r N\left(\frac{K-N}{K}\right)$ Rate of change of population density

$N=$ Population density at time

$N=$ Population density

$r=$ Intrinsic rate of natural increase

$K=$ Carrying capacity

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Population growth curve $A$ when resources are not limiting. Plot is exponential or geometrical curve $B .$ When resources are limiting the growth, plot is logistic

$^{\prime} K^{\prime}$ is carrying capacity

A population growing in a habitat with limited resources shows three phases.

$(i)$ Lag phase It is the initial phase in which a population adapt themself according to the environment and starts to increase their number

$(ii)$ Log phase It is the second phase in which a population use its resources maximally and increases their number exponentially. Number of birth $>>$ Number of death

$(iii)$ Stationary phase It is the $3^{\text {rd }}$ phase in which the population reached the carrying capacity level and population get stationary position. No of death $=$ No of death

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