Final answer:
Density-dependent factors are biotic and vary with population density, increasing effects like competition and predation, while density-independent factors impact population numbers regardless of density, such as pesticide use or extreme weather.
Step-by-step explanation:
Density-dependent and density-independent factors are both environmental conditions that impact population numbers. Density-dependent factors, which are mostly biotic, vary in their effects on populations depending on the population density. For instance, as a population becomes denser, the effects of predation, competition, waste accumulation, and diseases often intensify, leading to a higher mortality rate. An example would be that with increasing population density among caterpillars, food sources become scarcer, causing a decline in population due to starvation or reduced reproductive rates.
In contrast, density-independent factors impact the population regardless of its density. These are typically abiotic factors such as natural disasters, extreme weather conditions, or human activities like pesticide use. For example, the application of a pesticide will reduce a caterpillar population whether it is large or small because it kills caterpillars indiscriminately.
Interaction of Density-Dependent and Density-Independent Factors
These factors can interact in complex ways. For instance, a drought (a density-independent factor) might reduce a plant population, which in turn diminishes the food supply for a herbivorous insect population, leading to increased competition for food, a density-dependent factor. Thus, the combined effects can cause a more dramatic decline in the insect population than would either factor alone.