Which of the following scenarios would lead to a decrease in population density in a given habitat?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Both the death rate and the emigration rate are high.
Population density changes through four processes. Natality (births) and immigration (individuals coming in) add to the population. Mortality (deaths) and emigration (individuals leaving) take away from it. The density falls when deaths plus emigrants are more than births plus immigrants.
Option (1) The birth rate is higher than the death rate. — Incorrect. When births are more than deaths, more individuals are added than lost. The density increases.
Option (2) More individuals are moving into the habitat than leaving it. — Incorrect. When more individuals move in than leave, immigration is more than emigration. This also increases the density.
Option (3) Both the death rate and the emigration rate are high. — Correct. High deaths and high emigration are the two processes that decrease density. With both high, individuals are lost from the habitat faster than they are added.
Option (4) Both the birth rate and the immigration rate are high. — Incorrect. Births and immigration are the two processes that add individuals, so high values of both raise the density.
NCERT Extract:
Population Growth – “… Whatever might be the ultimate reasons, the density of a population in a given habitat during a given period, fluctuates due to changes in four basic processes, two of which (natality and immigration) contribute to an increase in population density and two (mortality and emigration) to a decrease.”