(a) Study the flow chart given below and complete the equation that follows by identifying 1, 2, 3 and 4.

(b) Mention the different ways by which the population density of different species can be measured.

Explanation

(a) `N_(t+1) = N_(t) + {(1+2)-(3+4)}`
`N_(t+1)=N_(t)+{(B+I)-(D+E)}`
`N_(t)` = Population density at time t
B = Natality
I = Immigration
D = Mortality
E = Emigration
Population density will increase if the number of births plus the number of immigrains (B+I) is more than the number of deaths plus the number of emigrants (D+E), otherwise it will decrease.
(b) Population density means, number of individuals present per unit area, population density can be measured by determining the population size, the different methods to study population density are as follows :
1 Percent cover biomass : In an area with 200 parthenium plants and only one banyan tree with large canopy, the density of banyan tree is small but does not reflect its important role in the community. Here, present cover or biomass is a more meaningful method of assessing population density.
Total Number : It involves physically, counting of organisms in the given area.
3. Relative Density : In this method there is no need to count the organisms individually.
Example : The number of fishes per trap gives the measure of their total density in a given water body.
4. Indirect Assessment : The tiger census is based on pug marks and foecal pellets.