title: Trophic omnivory across a productivity gradient: intraguild predation theory and the structure and strength of species interactions.
abstract: Intraguild predation theory centres on two predictions: (i) for an omnivore and an intermediate predator (IG-prey) to coexist on shared resources, the IG-prey must be the superior resource competitor, and (ii) increasing resource productivity causes the IG-prey's equilibrium abundance to decline. I tested these predictions with a series of species-rich food webs along New Zealand's rocky shores, focusing on two predatory whelks, Haustrum haustorium, a trophic omnivore, and Haustrum scobina, the IG-prey. In contrast to theory, the IG-prey's abundance increased with productivity. Furthermore, feeding rates and allometric considerations indicate a competitive advantage for the omnivore when non-shared prey are considered, despite the IG-prey's superiority for shared prey. Nevertheless, clear and regular cross-gradient changes in network structure and interaction strengths were observed that challenge the assumptions of current theory. These insights suggest that the consideration of consumer-dependent functional responses, non-equilibrium dynamics, the dynamic nature of prey choice and non-trophic interactions among basal prey will be fruitful avenues for theoretical development.
authors.affiliation: Department of Ecology and Evolution, University of Chicago, Chicago, IL 60637, USA. mark.novak@science.oregonstate.edu
authors.forename: Mark
authors.initials: M
authors.lastname: Novak
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D003163:Competitive Behavior; D005247:Feeding Behavior; D020387:Food Chain; D049851:Gastropoda / Q000502:physiology*; D009520:New Zealand; D011157:Population Dynamics; D011235:Predatory Behavior
keywords: adaptive foraging; alternative prey; consumer-dependence; handling times; interaction strength; per capita attack rate