What is population growth? Explain factors responsible for fluctuating population density.

Explanation

Population growth : The size of population of any species in not a static parameter. It keeps on changing with time, depending on various factors such as availability of food, predation pressure and prevailing weather. Such changes give some idea of what is happening to the population, whether it is increasing or decreasing. Though a number of factors affect population size, the density of a population in a given habitat during a given period, fluctuates due to four basic processes-natality, mortality, immigration and emigration. The population density is the number of individuals of a species per unit area/space at a given time. Mathematically population density is expressed as :
`D=(N )/(S )`
where, D stands for the population density, N denotes the number of individuals of a species at a specific time and S represents the number of units of the space.
(i) Natality : It refers to the number of births during a given period in the population that are added to the initial density.
(ii) Mortality : It is the number of deaths in the population during a given period.
(iii) Immigration : It is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.
(iv) Emigration : It is the number of individuals of the same species Immigration who have left the habitat and gone elsewhere during the time period under consideration. Natality and immigration contribute to an increase in population density, while mortality and emigration to a decrease.

Therefore, population growth or change in the size of population in a given time is determined by the above factors. Change in population size = (Total Birth + Immigration ) - (Total Death + Emigration)
If N is the population density at time t, then its density at time
`t+1 `is
` N_(t+1) =N_t +[(B+1)-(D+E)]`