Observe the given figure representing different are pyramids for human population answer the following question.

Identify the correct statements from the following:

(A) Population size can be estimated indirectly
(B) The only measure to know the population size is to count the number of individuals
(C) Tiger census is often based on the number of animals or humans killed
(D) Tiger census is often based on pug marks and fecal pellets

Choose the correct answer from the options given below:

(A) and (D) only

The correct answer is Option (2) → (A) and (D) only

Population size, more technically called population density (designated as N), need not necessarily be measured in numbers only. Although total number is generally the most appropriate measure of population density, it is in some cases either meaningless or difficult to determine.

Sometimes, for certain ecological investigations, there is no need to know the absolute population densities; relative densities serve the purpose equally well. For instance, the number of fish caught per trap is good enough measure of its total population density in the lake. We are mostly obliged to estimate population sizes indirectly, without actually counting them or seeing them. The tiger census in our national parks and tiger reserves is often based on pug marks and fecal pellets.