Prey selection of a shell-invading leech as predicted by optimal foraging theory with consumption success incorporated into estimation of prey profitability

1. Optimal foraging theory assumes that a predator preys selectively to maximize fitness gain. The associated model assesses predator’s fitness gain by estimating prey profitability in terms of appropriate foraging costs and benefits. While model developing, unsuccessful foraging was included in the model because it is inevitable and costly for a predator. However, it has rarely been taken into account in previous studies, nor has the consumption success been included in the estimation of prey profitability. Thus, although such model may successfully predict prey selection of many predators, it is inadequate in explaining prey selection of predators with highly variable consumption success. 2. In this study, we tested the prediction of optimal foraging model by accounting for consumption success in prey profitability for the prey selection of Whitmania laevis (Hirudinida: Hirudinidae), a shell-invading leech with highly variable consumption success in different prey. Five snail species, including three operculated species and two non-operculated species, were used as prey. 3. Our results showed that W. laevis exhibits prey-size selection. Leeches consumed more medium-sized snails among operculated species and more large-sized snails among non-operculated species, and the selection fitted the prediction of prey profitability by accounting for consumption success. Leeches also practiced prey-species selection, but such selectivity was confined to non-operculated species rather than snails with higher profitability. 4. Our study showed that when the consumption success was incorporated into the estimation of prey profitability, the optimal foraging model could, as predicting the prey-size selection of W. laevis, predict the prey selection of a predator with highly variable consumption success, which has been poorly predicted previously. This could also be the case for other predators with variable consumption success in future studies.