Which type of population becomes more efficient in all work?

If a population has just been established in an ecosystem,which of the following factors will have the greatest impact?

"Population is an auto-regulated system" was said by

Bell-shaped age pyramid indicates that

The density of a population in a habitat per unit area is measured in different units. Write the unit of measurement against the following:
$(a)$ Bacteria $.......................$
$(b)$ Banyan $ .......................$
$(c)$ Deer $ .......................$
$(d)$ Fish $ ......................$

List any three important characteristics of a population and explain.