In botanical epidemiology (i.e. the study of plant disease dynamics) regulation typically is considered to come from two sources; either, or both, of which may be important in a particular case. Endogenous regulation is more or less synonymous with density-dependence and plant disease epidemiologists generally mean by that term, that one or more of the per capita rates affecting population increase is dependent on current population density (so all of the complexities and potential ambiguities mentioned in Corey's excellent review are on display in our literature). Exogenous regulation is typically ascribed to human attempts to limit the intensity of disease. Personally, I think the ideas of Royama and Turchin are of particular value in practical understanding of biological population dynamics generally but since they don't deal with plant diseases explicitly their work is not widely known in the botanical epidemiology community.

Regulation involves any biotic or abiotic factor that may be working with one another that lessens the density of a population.