Fig. 2.

Model results of changing densities of producers (green), host herbivores (black), adult parasites (orange), and parasite propagules (gray; not visible because of adult parasites) in the environment under varying scenarios of parasite effects on hosts. Simulations shown are (A) without parasites, or with parasites that have negative intensity-dependent effects on (B) survivorship, (C) host resource intake, or (D) fecundity (note that parasite population is >0). The model was parameterized with values corresponding to the producer–caribou–Ostertagia system (Table 1) with herbivores, adult parasites, and free-living stages of the parasite expressed as number per square kilometer and producer biomass expressed in kilograms per square kilometer. The density values are visualized as relative to the maximum of each group in each panel.