Q.Distinguish between natality and mortality, and between immigration and emigration, as the four factors that change population size.

Realized mortality is the actual number of deaths occurring in a population under the real, existing environmental conditions/pressures.

In population ecology, mortality (death rate) is described using two complementary terms: absolute (or minimum/theoretical) mortality refers to the deaths that would occur even under the most ideal conditions, purely due to old age/physiological limits, whereas realized mortality is the actual, observed number of deaths that occur in a population when it is subjected to real, prevailing environmental pressures such as predation, disease …

Absolute (or maximum/potential) natality is the theoretical maximum number of births possible under ideal, unrestricted conditions.

In population ecology, natality (births) is described in two ways: absolute natality (also called maximum or potential natality) is the theoretical maximum number of offspring produced under ideal conditions with no limiting factors, whereas realized natality is the actual number of births that occur under the real, existing environmental conditions (which is always lower). Mortality …

Emigration is out-migration that reduces a population's size.

Emigration refers to individuals permanently leaving their original population and moving to settle in a different geographic area or population. Along with mortality, it is one of the two processes that decrease population size (the other two, natality and immigration, increase it). Emigration is often triggered by overcrowding, resource scarcity, or competition, and it reduces population density in the area vacated while potentially founding or aug …