PARENT SESSION
Contributed Oral Session 3: Herbivory: Plant - Herbivore Interaction
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 513 E, Level 5, Palais des congrès de Montréal

Population dynamics of Aphis nerii and A. asclepiadis on milkweed (Asclepias syriaca): Influences of plant resistance traits, mutualists, and predators.

Mooney, Kailen^*,1, Agrawal, Anurag¹, ¹ Cornell University, Ithaca, NY, USA

ABSTRACT- Species that coexist in ecological communities are thought to exhibit trade-offs in fitness-enhancing traits, thereby favoring species in some environments, but not others. In this study we examine the ecological diffferences between two closely related aphid species, Aphis nerii and A. asclepiadis, that share the same host plant, common milkweed (Asclepias syriaca), and that co-occur throughout much of the host plant's range. Aphis nerri is a brightly colored aposomatic species with a very high R_max, while A. asclepiadis is cryptic and has a much slower population growth rate. In laboratory and field experiments we show that these ecological differences extend to variation in the strength of density dependence, relationships with mutualistic ants, and ability to sequester defensive cardenolides from the host plant. Heritable resistance traits of the host plant also influenced the population dynamics of both Aphis species. Thus, coexistence of these two aphids, which utilize the exact same resource, may be facilitated by difference in multi-trophic interactions with host plants, predators and mutualists.

Key words: mutualism, coexistence, herbivory, predation