Continuous host mortality
In the second scenario, we parameterized a negative exponential function of snail size on predator attack rate, pA , based on laboratory feeding trials across a range of prawn and snail sizes (Sokolow, Lafferty, and Kuris 2014). We held the handling time,pH , independent of snail size. Biologically, this assumption corresponds to predators being equally likely to contact and handle any snail, but larger snails more frequently escape these encounters without being eaten. These feeding data reported snail wet weights, which we converted to length (mm) using a size relationship of length to mass (L3) (Thompson 1988)
\begin{equation} h_{t}=h_{b}+\frac{p_{A}\ \ p_{N}}{1+\ p_{A}{\ \ p}_{H}\ \ {\ H}_{N}}e^{-0.237\ \ L_{i}}\ \nonumber \\ \end{equation}
where Li is individual host length (mm). Our previous analyses of the underlying SIDEB model show resource productivity interacts with sources of snail mortality to drive parasite output rates. Therefore, we simulated a range of resource supply rates of 0, 0.01, 0.05, 0.1, 0.2, and 0.25 for algae (d–1) and detritus (mg C L–1 d–1). We varied resource growth rates for each resource type as separate simulations (n = 5). Complete and reproducible model code is found in Appendix 2.