PARENT SESSION
Contributed Oral Session 143: Predator - Prey Ecology: Intraguild Predation and Community Dynamics
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 522 A, Level 5, Palais des congrès de Montréal

Apparent competition among prey leads to intraguild predation among predators.

Harvey, Chad^*,1, Ives, Anthony¹, ¹ University of Wisconsin-Madison, Madison, WI

ABSTRACT- Indirect interactions within a food web can arise when two prey species share a natural enemy or two natural enemy species share prey. The objective of this study was to assess if the occurrence of one indirect interaction, apparent competition among two prey species (pea aphid and soybean aphid), affects a second indirect interaction, intraguild predation among a generalist and a specialist natural enemy. Results from a three spatial-scale study, showed that pea aphids are negatively affected via apparent competition with soybean aphids, mediated by the ladybeetle, Harmonia axyridis. Pea aphids are also attacked by the specialist parasitoid Aphidius ervi. In a controlled mesocosm experiment, we found parasitism of pea aphids by A. ervi significantly decreased from 18% in the presence of soybean aphid or H. axyridis alone, to 6% in the combined presence of soybean aphid and H. axyridis. Furthermore, there was a significant decline in A. ervi survival, suggesting increased intraguild predation of H. axyridis on A. ervi. The results of this study indicate that an indirect interaction among prey species can increase the intensity of an indirect interaction among natural enemies.

Key words: indirect interactions, apparent competition, intraguild predation, food web complexity