PARENT SESSION
Contributed Oral Session 72: Trophic Systems: Communities; Predator Behavior
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 524 C, Level 5, Palais des congrès de Montréal
Big things rule the world: Predators are more important than endophytic fungi in regulating aphid populations.
Haerri, Simone*,1, Mueller, Christine1, 1 Institute of Environmental Sciences, Zurich, Switzerland
ABSTRACT- Top-down (natural enemies) and bottom-up (resources) forces work in concert to structure populations and communities. Many grasses enter symbiotic associations with fungal microorganisms, because the otherwise weakly protected grasses benefit from induced herbivore resistance through fungus derived alkaloids. To assess the relative importance of the presence of endophytic fungi versus the effects of natural enemies on aphid populations, a field experiment of a 4 x 2 full factorial design was carried out with four levels of predator treatments and two levels of endophyte infection. Predator presence significantly reduced the density of two common grass aphids, Rhopalosiphum padi and Metopolophium festucae, whereas the presence of the endophytic fungi only reduced M. festucae densities. Overall the predator effects on aphid population growth were much stronger than effects through mycotoxins produced by the grass symbionts. These results suggest that top-down effects by natural enemies on aphid communities are significantly stronger than bottom-up effects of endophytes. Understanding the mechanisms by which herbivore abundance is changed and by which different species of herbivores interact in the presence of symbiotic fungi will further our understanding about critical forces structuring natural communities.
Key words: endophytic fungi, multitrophic interactions, aphids, top-down vs. bottom-up