Omnivory and spatial dynamics reduce adverse effect of intraguild predation on herbivore suppression [abstract]

Most terrestrial food webs include intraguild (IG) predators, which feed on herbivores as well as other predators in the system. In general, IG predators have been shown to suppress intermediate predator populations, allowing herbivore densities to increase. Yet many of the interacting predators are in fact omnivores that feed on prey as well as plant-based foods, such as flower pollen. We therefore hypothesized that omnivorous feeding acts to reduce the adverse effect of intraguild predation (IGP) on herbivore suppression and lessen plant damage. That pollen becomes available on some plant structures (flowers) but not others, adds another important level of complexity to these systems. We tested these trophic interactions in a system that consisted of strawberry plants, western flower thrips (WFT, Frankliniela occidentalis) and two of its predators, the mite Neoseiulus cucumeris and the bug Orius laevigatus. All three consumers feed on strawberry pollen, WFT damages strawberry fruits, the mite preys on 1st instar WFT, and the bug feeds on WFT and the mites. Results show that (i) significantly fewer WFT were killed by the predators in the presence of pollen than in its absence; (ii) predation on N. cucumeris by O. laevigatus (i.e., IGP) was significantly lower in the presence of pollen than in its absence; (iii) in the presence of pollen, WFT and both predators primarily reside in flowers rather than fruits and leaves; (iv) In the absence of pollen, WFT were recorded primarily on fruits; (v) In the presence of pollen, N. cucumeris is found in the flowers only when O. laevigatus is absent; else, the mites are found on the fruits or leaves; and (vi) When both predators are present, significantly lower fruit damage was observed in the absence of pollen than in its presence. Taken together, results show that omnivorous feeding and differential response to spatially heterogeneous resources buffer strong herbivorous and IG predatory interactions. This may allow for complex trophic interactions, such as omnivory and IGP, to persist and be common in nature.