question_answer 16)

With the help of suitable diagram describe the logistic population growth curve. 

Answer:

                Logistic population growth curve or S-shaped or sigmoid growth curve is shown by the yeast cells grown under laboratory conditions. It is also shown by the populations of most organisms. It has 5 phases: lag phase, positive acceleration phase, exponential phase, negative acceleration phase, and stationary phase. In lag phase there is little or no increase in population, hi positive acceleration phase increase in population starts and occurs at a slow rate in the beginning.                 During exponential phase, increase in population becomes rapid and soon attains its full potential rate. This is due to the constant environment, to the availability of food and other requirements of life in plenty, to no predations and interspecific competition and to no serious intraspecific competition so that the curve rises steeply upward. Whereas in negative acceleration phase, the growth rate finally slows down as environmental resistance increases.                 Finally, the population becomes stable during the stationary phase because now the number of new cells produced almost equals to the number of cells that die. Every population tends to reach a number at which it becomes stabilized with the resources of its environment. A stable population is said to be in equilibriums, or at saturation level. This limit in population is a constant K and is imposed by the carrying capacity of the environment.                 S-shaped curve is also called Verhulst-Pearl logistic curve. The sigmoid growth form is represented by the following equation:                                 where  rate of change in population size                  intrinsic rate of natural increase                  population size;  carrying capacity                  environmental resistance