Examples of Density Dependent Factors

Density dependent factors are events that impact a biological environment, the measured effects of which are relative to the pre-existing population size, or density. They differ from density independent factors in that the latter are precipitated by non-living abiotic factors, such as weather conditions or natural disasters that will effect the entire population regardless of number. In contrast, density dependent factors are biotic in origin, generated by living organisms and producing effects inversely proportional to population size.

Disease

• The outbreak of bacterial or viral disease is one of the best examples of density dependent factors that are reliant on population concentration in terms of impact. In short, the greater the density of the existing population, the greater the influence the disease will have on that population. This is because highly dense populations are more likely to contain inhabitants living in close proximity to each other than living far apart, making the likelihood of each living entity to become infected with the disease much greater. Another factor that illustrates density dependence is population diversity. An environment containing many different species of living organisms is also more likely to be effected by disease due to dense cohabitation.

Predation

• The relationship between predator and prey is an excellent example of nature’s own system of population stabilization. For the predator, the opportunity to thrive exists in areas where the population of prey is the greatest. Naturally, as long as the food source is plentiful, the predator remains in the environment. At the same time, however, the prey in question responds by producing more offspring to re-establish the population of its own species. However, since most predators are likely to become the prey of another species, its population will also be effected. This balance between predator and prey population illustrates the concept of how the effects of density dependent factors are inversely proportional to population size. The denser the population, the slower its growth rate, and vice versa.

Parasitism

• Parasites also produce a density dependent effect on a population. The greater the population density, the more opportunity parasites have of moving from host to host to ensure their own survival. However, since parasites thrive by stealing nourishment from their hosts, the latter are more likely to decline in number due to starvation, delayed reproduction, or disease.

Competition

• There are two examples of density dependent factors that fall under this category: Interspecific competition and intraspecific competition. Interspecific competition refers to competition between species to dominate the same habitat. Resources that two or more species may compete for include suitable nesting sites and food. Intraspecific competition refers to members of the same species competing for resources within the same environment.