Question

A biologist studies the population of rats in a barn. He found that the average mortality was 240, average natality 250, immigration 20 and emigration 30.The net increase in population is
(a)10
(b)15
(c)05
(d)zero

Answer 1

Hint: The normal growth, size and development of a population depend upon the balanced interaction between three sets of natural forces; biotic potential and environmental resistance, natality and mortality and immigration and emigration. If there occurs stationary growth the number of individuals added to the population may be almost equal to the number of lost individuals.

Complete answer:
Zero population growth is also known as stationary growth. In this population remains almost static or stationary, without appreciable net gain or net loss in the total number of members. Zero growth occurs when natality and mortality are almost exactly counterbalancing and so are immigration and emigration also. Here the average mortality is 240, average natality 250, immigration 20 and emigration 30
$Natality+Immigration=\left( 250+20 \right) =270\cdot \cdot \cdot \left( 1 \right) $
$Mortality+emigration=\left( 240+30 \right) =270\cdot \cdot \cdot \left( 2 \right) $
$Net\quad increase\quad in\quad population\quad is\quad \left( 1 \right) -\left( 2 \right) =\left( 270-270 \right) =0$
Population growth is the increase in the number of individuals in a population. It is the rate at which the number of individuals in a population increases in a given time period.

Additional Information: -There are three kinds of population growth namely zero, positive and negative growth.
-In positive growth there will be an appreciable net increase in the size of population and also in the total number of its members.
-In negative population growth, there will be an appreciable net decrease in the size of population. It occurs when mortality is higher than natality and emigration is higher than immigration.
So, the correct answer is 'zero'

Note: -A groups of organisms of same or closely related species living together in the same geographical area with mutual interaction and genetic exchange is known as population.
-Populations occupying very small, restricted and often isolated areas or habitat patches are called local populations.
-Populations are never static , but are always dynamic in their size growth and composition.