Most predators exhibit saturating functional responses, their feeding rates becoming increasingly saturated as the abundance of their prey increases. In theory, such saturation is destabilizing, causing predator-prey dynamics to oscillate. Ecologists thus typically invoke low-density prey-switching to account for the empirical persistence and lack of cyclic dynamics in generalist predator-prey interactions. Using data from six New Zealand intertidal food webs, I ask to what degree the feeding rates of two whelk predators are saturated within the empirical context of their multispecies interactions.  I also determine the extent to which prey-attributes can be used to predict prey-specific contributions to the nonlinearity of a predator’s functional response, and investigate how a predator’s diet richness affects the degree to which it’s overall feeding rate is reduced by its prey. By extending and empirically parameterizing the classic Rosenzweig-MacArthur predator-prey model, I then ask whether the degree of saturation observed within New Zealand’s whelk populations is nonlinear enough to affect the stability of whelk-prey interactions, and how dynamics are affected by predator specialization.
Results/Conclusions

My results indicate that whelk feeding rates are generally not strongly saturated, that most prey contribute very little to their predator’s saturation, and that increasing diet richness has a non-additive effect on a predator’s saturation such that the addition of alternative prey has a stabilizing effect on predator-prey dynamics.  I thereby offer a unappreciated mechanism by which generalist predators stabilize the dynamics of species-rich food webs which does not rely on density-dependent prey-switching, and an explanation for why predator-removal experiments typically result in linear prey responses despite the inherent nonlinearity of trophic interactions.