The main direct and indirect interactions among second trophic level herbivores, omnivores in the third trophic level, and omnivorous fourth trophic level consumers foraging on a shared plant resource. Solid arrows indicate consumer-resource interactions whereas dotted ones indicate indirect interactions, such as interspecific competition. For simplicity, other interactions such as intraguild predation, apparent competition, and prey defensive responses are not illustrated. See text for detailed explanations.