Density-dependent factors are those that become limiting when the population density reaches a certain level, meaning their effects increase as the population size increases. These factors typically include predation, parasitism, disease, and competition.
Among the options provided, "Natural disasters" and "Human Activities" are density-independent factors because their impacts on the population do not depend on the population size.
Therefore, the answer is:
Natural disasters (or Human Activities, both are correct in context as they are density-independent factors).
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