Fig. 3.

Two-parameter diagrams illustrating the qualitative behavior of the mechanistic model (Fig. 1), which oscillates in the absence of disease. Panels display variation in the magnitude of parasite virulence for pairs of lethal (survival) and sublethal (fecundity, resource intake) components included in the model (log₁₀-transformed, setting the third component to zero). Parasites that harm any combination of host survival and resource intake consistently stabilize oscillations (gray; B). In contrast, parasites that harm host fecundity generate producer–host–parasite oscillations (orange), even in combination with a component of virulence that is otherwise stabilizing (A and C). The model is parameterized with values corresponding to the producer–caribou–Ostertagia system (Table 1).