Periodic departure and return of an individual in a population is known as

The different age groups in a population are classified by:

Under normal conditions,..................... are the most important factors influencing population density.

Geometric representation of age structure is a characteristic of

$(a)$ Label the three tiers $1, 2, 3$ given in the above age pyramid.
$(b)$ What type of population growth is represented by the above age pyramid?

If natality is represented by $B$,mortality by $D$,immigration by $I$,emigration by $E$,and population density by $N$,then the population density at time $t+1$ is represented by: