In population demography, which two processes can cause a population’s size to decrease?

• A. Increased natality and immigration
• B. Decreased mortality and increased natality
• C. Increased immigration and decreased emigration
• D. Increased mortality and emigration

Answer: (D)

Verified step by step guidance

1. Understand that population size changes based on four main processes: natality (birth rate), mortality (death rate), immigration (individuals moving into a population), and emigration (individuals moving out of a population).
2. Recognize that an increase in natality or immigration adds individuals to the population, causing it to grow rather than decrease.
3. Identify that a decrease in mortality means fewer individuals die, which would increase population size, not decrease it.
4. Focus on the processes that reduce population size: increased mortality means more individuals die, and increased emigration means more individuals leave the population.
5. Conclude that the two processes that cause a population’s size to decrease are increased mortality and emigration.