a) The size of the population tells us a lot about its status in the habitat.Whatever ecological processes are to be investigated in a population, be the outcomes of completion with another species, the impact of a predator, it is evaluated in terms of change in the population size.
b) Population size more technically called population density. Population size of a species is the number of individuals of a species per unit area volume.
`=(“Number of individuals in a region “N)/(“Unit area in a region”(S))`
`rArr P_(Delta) = N/S`
A population at any given time is compound of individuals of different ages. When the age of distribution (per cent individuals of a given age or age group) is plotted for the populations, the resulting structure is called age pyramid.