Which of the following is a biotic factor that affects population?

Step 1: Analyze the question The question asks for a biotic factor that affects population size. Biotic factors are living components of an ecosystem, while abiotic factors are non-living physical or chemical components.

Step 2: Explain the concept

• Biotic factors are living things and their interactions, such as predation, competition, parasitism, disease, and food supply from other organisms.
• Abiotic factors are non-living, such as temperature, water, salinity, light, pH, and soil type.
• Space is generally treated as a physical or limiting resource (abiotic). It is not a living thing, although competition for space involves organisms.

Step 3: Go through the options

• A. Predator: a living organism that hunts and kills prey, which reduces the prey population. Biotic.
• B. Salinity: the salt concentration of water. Abiotic.
• C. Space: a physical resource. Abiotic (competition for it is a biotic interaction, but space itself is not a living factor).
• D. Temperature: a physical condition. Abiotic.
• E. Water: a non-living resource. Abiotic.

Step 4: Answer The only living factor is the predator, so the correct option is A.

Exam tip: Ask yourself, "Is it alive, or does it come from something alive?" If yes, it is biotic. Predators, parasites, pathogens, competitors, and food organisms are biotic. Temperature, water, light, salinity, pH, and space are abiotic. Remember: bio = life.