Discrete host mortality
Increasing predator density triggered overcompensation in total cercariae output from infected hosts for both algae (Fig. 1) and detritus (Fig. 2) resource scenarios. For algae, compared to no predators (Fig. 1A), intermediate predator density generated peak parasite outputs (Fig. 1B) before a successful predator threshold eliminated infected hosts and parasites (Fig. 1C). Increasing predator density promoted higher parasite yields until an intermediate density of 10 N m–2, after which predator densities > 13 N m–2 successfully eliminated infected hosts and parasites (Fig 1D). Similarly, for detritus, mean cumulative parasite output peaked at 7 N m–2 before successful predator densities of > 14 N m–2 (Fig. 2).
Low (1 N m–2) to moderate (10 N m–2) predator densities consistently failed to suppress parasite output from all host size classes for both algae and detritus (Fig. 3). Here, targeting small- to medium-sized hosts between 0 and 15 mm was unsuccessful in mitigating parasite emergence irrespective of predator stocking density. That is, targeting infected juvenile and adult hosts <15 mm failed to control cercariae emergence for both algae and detritus. In contrast, targeting large adult hosts >15 mm successfully eliminated parasites for stocking predators >10 N m–2, demonstrating a minimum threshold needed to control parasite output. Combined, this unimodal backfire response of increasing control pressure prior to reaching a sufficiently intense measure illustrates the risk of moderate intervention.