Conclusions
Our results urge caution when implementing gape-limited biocontrol in
parasite transmission systems that meet similar conditions to these
prawns, snails, and schistosomes. Resource uptake by intermediate hosts
that increases transmission, intense resource competition among hosts,
and size-selective predators are all ingredients for potential
biocontrol failure that may also worsen with greater effort. Here, we
illustrate how resource competition as an underlying mechanism pervades
trophic levels and population changes to drive potentially
counterintuitive outcomes in the control of a major human parasite.
Overcompensation as a key element of these systems is emerging as a
recurrent theme in the ecology of pest control (Choisy and Rohani 2006;
Bolzoni, Real, and De Leo 2007; De Roos et al. 2007), resulting in a
growing list of scenarios that suggest ‘do or do not’ management
responses. Importantly, we emphasize that not adopting this strategy
does not suggest predatory biocontrol is hopeless, but rather weak or
inconsistent control efforts seem unlikely to succeed. One critical
management suggestion is that control programs should start small so
that effort can be sustained and gradually expanded, rather than spread
too thin. Ultimately, we stress the clear need for more experimental
testing of predator biocontrol of human schistosomes and encourage more
physiology and ecology detail in pest management more broadly. These
details legitimise the biological data needed for successful control
design that can extend to other host-parasite systems.