If $10$ individuals in a laboratory population of $50$ fruit flies die during a week, then the death rate during this period is $= ........$ individuals per fruit fly per week.

Which of the following factors regulate human life with reference to population density?

Under a particular set of selection pressure,organisms evolve towards the most efficient reproductive strategy. For example:
$A$) Oysters produce a large number of small-sized offspring.
$B$) Mammals produce a small number of large-sized offspring.
In the light of the above statements,choose the correct option.

Define the following terms:
$(1)$ Immigration
$(2)$ Emigration
$(3)$ Mortality

Which of the following formulas is used to determine natality?

The effect of various factors on a population is reflected in its size,which can be expressed by .......