PARENT SESSION
Thursday, August 10, 1:30-5:00 pm
COS 94 - Plant-herbivore interactions II
Ballroom E, Ballroom Level, Cook Convention Center
Presiders: C Sagers

Individual and combined influence of predators and heritable plant traits on arthropod communities of common milkweed (Asclepias syriaca).

Mooney, Kailen^*,1, Agrawal, Anurag¹, ¹ Department of Ecology and Evolutionary Biology, Ithaca, NY, USA

ABSTRACT- Both plant traits and predators can shape arthropod community structure, but it is currently unclear how these two factors work in combination. The interaction between plant genetic variation and predation may affect herbivores via ecological and evolutionary dynamics. We used a quantitative genetic design to measure the effects of heritable traits of milkweed (Asclepias syriaca) on resident arthropod communities, and whether components of the arthropod community itself were extended phenotypes of the plant. These questions were addressed in the presence and absence (exclusion) of the ant Formica podzolica, a predator of some arthropods and a mutualist of others. In the absence of ants, the abundance of several arthropod groups was heritable and their abundances were correlated with specific (but differing) heritable plant traits. In the presence of ants, the abundances of most arthropod groups declined and were not heritable, and they were not correlated with plant traits. We speculate that ants cause a shift in arthropod behavior from foraging for optimal resources to foraging in enemy-reduced conditions. Predation thus masked or trumped the consequences of plant genetic variation. Thus, if feeding by herbivores carries a fitness cost to milkweed, we predict that selection by herbivores on plant traits will only be realized in the absence of ants.

Key words: herbivory, predation, arthropod community ecology