Population Growth

The size of a population of a species keeps on changing from time to time depending on various factors such as weather, food availability, and predation pressure. Therefore the density of the population changes during a given period due to changes in four basic processes two of which (natality and immigration) contribute to an increase in population and the other two (mortality and emigration) contribute to the decrease in population.

• Natality: It refers to the number of birth rates during a given period in the population that are added to the initial density. The birth rate is also known as Natality. It is the rate of birth, germination, or vegetative propagation of an individual.

Natality = Number of births per year / Number of population per year * 1000

• Immigration: It refers to the number of people of the same species has shifted into the habitat from elsewhere during the time period under consideration. It leads to an increase in the size of the population rate. It is an inward movement. Thus, it contributes to population explosion.
• Mortality: It is defined as the death rate per thousand people in the population during a given period or per year. It leads to a decrease in the population size. It is calculated on the basis of the deaths in a particular area. The death rate is also known as Mortality.
• Emigration: It indicates the number of people of the same species who left the habitat and went elsewhere from the population during the time period under consideration. It leads to a decrease in the size of the population rate. It is an outward movement. Thus, it helps to prevent a population explosion.

N is the population density at time t, then density at time t+1 is 

N_{t+1 = Nt + [(B + I) – (D + E)]}

Population Density will increase if the number of birth plus the number of immigrants (B + I) is more than the death plus the number of emigrants (D + E). 

Population Growth: Population growth refers to the increase in the number of people in a given area in a particular period of time. It is the main cause of this world because the population of human beings is not a static factor. Population growth depends on various factors such as weather, food availability, and predation pressure. The density of population changes during a given period due to changes in four basic processes two of which natality and immigration contribute to an increase in population and the other two mortality and emigration contribute to the decrease in population.