Trophic omnivory across a productivity gradient: intraguild predation theory and the structure and strength of species interactions |
| |
Authors: | Mark Novak |
| |
Affiliation: | 1.Department of Ecology and Evolution, University of Chicago, Chicago, IL 60637, USA;2.Department of Zoology, Oregon State University, Corvallis, OR 97331, USA |
| |
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. |
| |
Keywords: | interaction strength per capita attack rate alternative prey handling times adaptive foraging consumer-dependence |
|
|