PARENT SESSION
Thursday, August 10, 1:30-5:00 pm
OOS 14 - Ecological stoichiometry of terrestrial animals
Ballroom D, Ballroom Level, Cook Convention Center
Organized by: AD Kay (adkay@stthomas.edu), S Bertram, and J Schade
This session will examine the degree, causes, and ecological consequences of differences in elemental composition among terrestrial animals.
Plant-provided carbohydrates mediate the aggressiveness of ant bodyguards.
Ness, Josh*,, Bronstein, J.L.1, Morris, W.F.2, 1 Skidmore College, Sarataoga Springs, NY2 University of Arizona, Tucson, AZ
ABSTRACT- Animal foraging has been characterized as an attempt to maximize the intake of Carbon and Nitrogen at appropriate ratios. Plant species in over 90 families produce carbohydrate-rich extrafloral nectar (EFN), a resource attractive to ants and other omnivorous insects. This attraction can benefit the plant if those arthropods subsequently attack herbivores. Here, we test the hypothesis that access to carbohydrates (C) increases the ants desire for meat (N) and hence the likelihood of attacking herbivorous insects on the host plant. This aggression hypothesis would be disproved if EFN was itself a sufficiently balanced food source, or if ants provided access to protein were more aggressive towards potential prey items than were ants provided access to carbohydrates. In the Ferocactus wislizeni cactus and ant system, C:N ratios of EFN exceeded that of ants or potential prey items by an order of magnitude (i.e., are an unbalanced food for ants). Baiting studies demonstrated that the most common species of ant attendants all recruit more workers to N-rich protein baits than to C-rich sugar baits, and that this difference was even more pronounced when the ants had access to F. wislizeni EFN. This suggests that meat is a more attractive resource than are carbohydrates in this environment, and that preferences can be altered by forager history. Ants provided access to supplemental carbohydrates responded more aggressively to surrogate herbivores than did control colonies (no additional resources provided) or colonies provided protein. The latter difference is contrary to that predicted by the ownership hypothesis (i.e., ants protect plants as valuable food resource), and suggests plant protection could be elicited by plant-mediated dietary imbalances.
Key words: mutualism, plant defense, foraging