15. With the help of suitable diagram describe the logistic population growth curve.
Logistic population growth curve
Growth of a population takes place according to the availability of food, presence of predators and parasites, presence of other biotic and abiotic factors affecting a population and other condition in a particular environment. There are two main types of models i.e. exponential growth model and logistic growth model.
Logistic growth curve represents the logistic growth model. It represents growth when there is a competition between the individuals of a population for food and space. In this case, the fittest organism survives, reproduces and population growth is seen. In this type of growth, initially, a lag phase is shown which is followed by phases of acceleration and de-acceleration. The different phases of the logistic growth curve are:
1. Lag phase- In this phase, no growth is seen due to the absence of food and other resources.
2. Positive acceleration phase- Limited growth in population is seen as the resources become available.
3. Exponential growth phase- The population grows suddenly and show very rapid growth. The curve rises steeply.
4. Negative acceleration phase- In this phase, environmental resistance increases and growth rate of the population decreases.
5. Stationary phase- In this phase, the growth becomes stationary and becomes stable. The population is said to have reached the carrying capacity of the habitat.
A diagrammatic representation of Population growth curves is given below. The curve a represents exponential growth and curve b represents logistic growth
The equation of the logistic growth curve is as follows:
Where N = Population density at time t
R = Intrinsic rate of natural increase
K = Carrying capacity
Since resources for growth for populations are finite and become limiting, the logistic growth model is considered a more realistic one.