Answer:
Growth rate.
Step-by-step explanation:
In biology, growth rate can be defined as the rate, at which the number of a populations of a particular area or region is increasing in a given period of time.
Growth rate represents that change in number of individuals of population over a period. It is expressed as percentage of the total organisms of a population during beginning of that time period.
Thus, the correct answer to be filled in the blank is growth rate.