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

Intraguild predation: Contribution of prey stoichiometry (carbon:nitrogen content) versus behavior to predator performance.

Denno, Robert^*,1, Matsumura, Masaya², Trafelet-Smith, Genevieve, ¹ University of Maryland, College Park, Maryland² National Agricultural Research Center, Kumamoto, Kyushu, Japan

ABSTRACT- Intraguild predation (IGP) is a widespread phenomenon in both natural and agricultural systems. Given its important consequences for prey suppression and food-web dynamics, understanding factors that underlie IGP is essential. Here we contrast two factors, namely prey stoichiometry (C:N) and prey behavior, as potentially important prey characteristics that influence the choice of prey by a predator. Recent data show that predators on average have a higher nitrogen content and lower C:N ratio than potential herbivorous prey. Thus, many predators may be nitrogen limited and intraguild predation may allow them to increase their nitrogen intake and growth by supplementing a diet of herbivores with more nitrogen-rich intraguild prey. Alternatively, predators may be more difficult to capture due to risks associated with attacking other predators. We tested these hypotheses using an assemblage of salt marsh-inhabiting arthropods. First, we determined the nitrogen content and C:N ratio of taxa in three trophic groups (plants, herbivores, and predators). Second we fed an intraguild predator, the wolf spider Pardosa, one of three diets (herbivores, intraguild prey, or a mix of the two) and measured spider survival, growth, capture rate, and biomass and nitrogen intake. Weight gain and nitrogen intake in Pardosa were highly correlated with the biomass of prey consumed. However, after accounting for the prey biomass consumed across all diet treatments, we found little evidence that either the N content or C:N stoichiometry of prey contributed to the growth of Pardosa. Thus, there was little support for the hypothesis that prey stoichiometry confers a performance advantage to Pardosa and in itself promotes IGP. In this system, behavioral characteristics of predators and prey play a significant role in prey capture and predator performance. Nonetheless, by supplementing their diet with intraguild prey, predators such as Pardosa can increase their nitrogen intake and performance.

Key words: Intraguild predation, predator performance, ecological stoichiometry, risk of predation