Which one of the following is a density-independent factor that limits the size of the natural population?

Correct option is C

Introduction
· Population regulation occurs through two types of limiting factors: density-dependent and density-independent factors.
· Density-independent factors affect the mortality or reproduction of a population regardless of how many individuals live in a given area.
· These factors are typically abiotic (non-living) and often related to sudden environmental changes or catastrophic events.

​Information Booster​

Severe drought is a density-independent factor because its occurrence and severity are not influenced by the number of individuals in the population.

Whether there are 10 individuals or 10,000 in an ecosystem, a severe drought will reduce the available water and food resources equally for all, leading to a population decline.

Unlike biological factors like competition, the impact of a drought is determined by external climatic conditions rather than the internal density of the population.
· Density-independent factors usually include natural disasters such as floods, fires, hurricanes, and extreme temperature fluctuations.
· These factors can cause a "population crash," where the number of individuals drops abruptly and significantly below the carrying capacity.
· While they do not regulate a population toward an equilibrium (like density-dependent factors do), they play a major role in determining the actual number of individuals present at any time.
· Most density-independent factors are climatic or anthropogenic (human-caused), such as habitat destruction or pesticide use.
· In r-selected species (like insects), density-independent factors often play a more dominant role in population control than density-dependent factors.

Additional Information
· Predation is a classic density-dependent factor; as the prey population increases, predators find them more easily, and the predator population itself may grow, leading to higher mortality rates in the prey.
· Territoriality is a density-dependent behavioral mechanism where individuals defend a space; as density increases, the availability of territories decreases, limiting the number of breeding pairs in the population.
· Sex ratio is an intrinsic demographic characteristic of a population; while it influences the reproductive potential and growth rate, it is generally considered a population parameter rather than an external density-independent limiting "factor" like a catastrophe.