The main difference between density-dependent factors and density-independent factors is that density-dependent factors affect only populations of certain sizes while density-independent factors affect populations in the same way, regardless of population size. Factors dependent on population density include illness, parasitism and scarcity of resources, while density-independent factors include weather phenomena, natural disaster and human activities, such as damming rivers and clearing forest areas and plains.
Density-dependent factors only impact societies when populations reach a certain size. Proximity of groups within a population impacts the effect of some density-dependent factors like diseases, which spread quickly in areas with dense concentrations. Competition, another density-dependent factor, occurs when living beings in given areas fight to gain access to dwindling vital resources such as food and water.