Which of the following will have the least effect on the rate of change of the numbers in a population

Analyze the question: We need the factor that has the least effect on how quickly a population's numbers rise or fall.

Concept: Population size changes mainly because of four things: natality (birth rate), mortality (death rate), immigration and emigration. Factors that strongly affect these are:

• Food supply: Scarce food leads to starvation, lower reproduction and migration. Plentiful food leads to growth. This has a large effect.
• Disease: Epidemics can kill large numbers quickly. This has a large effect.
• Predation: Predators directly reduce prey numbers, and predator and prey populations rise and fall together. This has a large effect.
• Mutation: Mutations are random changes in genes. They are rare, and most have little or no immediate impact on how many individuals there are. They affect genetic variation over long periods (evolution), not the short-term numbers in a population.

Solution:

• Food supply (B), disease (C) and predation (D) all directly change birth and death rates.
• Mutation (A) is infrequent and acts slowly, so its effect on population numbers is the smallest.

Answer: A. Mutation.

Tip: When a question asks for the "least effect" on population numbers, choose the factor that does not directly cause deaths, births or movement. Remember the main controls as the "food, foes, and fevers" (food, predators, disease), while mutation is a long-term genetic matter.