Concept:Population size is reduced by factors that increase deaths or lower survival, such as predation.
Explanation:Predation involves one organism consuming another, which directly removes individuals from the prey population.
Immigration brings new individuals into a community, so it increases population.
Mutualism benefits both species and generally supports population growth, not reduction.
Edaphic factors are soil conditions, which may affect population but are not the most direct reducing agent among the options.
Therefore, predation is the factor that can clearly reduce the population of a community.
Answer:C. predation