Question

Whatever might be the ultimate reasons, the density of a population in a given habitat during a given period, fluctuates due to changes in

• A. four basic processes—birth rate, death rate, sex ratio and age distribution
• B. two basic processes—immigration and emigration
• C. four basic processes—natality, mortality, immigration and emigration
• D. two basic processes—natality and mortality

Answer 1

The correct option is C four basic processes—natality, mortality, immigration and emigration

Population Density :
Population density refers to the number of individuals residing in a given area and population size refers to the number of individuals in a population. Population size technically is population density.

Factors affecting population density :
Population density fluctuates due to four major processes:

Natality: It is expressed as the number of births in a given population over a particular time period.

Mortality: It is expressed as the number of deaths in a given population over a particular time period.

Immigration: It is the number of individuals of the same species moving into an area/ habitat from elsewhere during a given period.

Emigration: It is the number of individuals of the same species moving out of an area/ habitat to elsewhere during a given period.

Natality (B) and immigration (I) increase the population density while mortality (D) and emigration (E) decrease the population density.

Attributes of population :
Population has certain attributes like birth rate, death rate, sex ratio and age distribution which are absent at the individual level.

Final answer :
(C) four basic processes—natality, mortality, immigration and emigration.