Intraguild predation promotes complex alternative states along a productivity gradient.

Intraguild predation is the simplest, ubiquitous form of trophic omnivory, known to greatly influence the structure and functioning of natural and managed food webs. Although alternative states are fundamental to intraguild predation dynamics, only necessary conditions for alternative states have been previously reported. Using simple models, we found complex but systematic patterns in which different alternative states occur along a productivity gradient, and clarified the sufficient conditions to separate these patterns. We found that two quantities known to control the necessary conditions also determine the sufficient conditions: (1) relative energy transfer efficiency through alternative trophic pathways to an intraguild predator, and (2) relative resource exploitation ability between intraguild prey and predator. These governing quantities suggest how body size and stoichiometric relations between intraguild prey and predators can influence the possibility of alternative states. Our results indicate that food webs involving intraguild predation have a high potential of complex alternative states, and their management can be highly precarious.