PARENT SESSION
Oral Session # 84: Trophic Structure II: Terrestrial and Aquatic Systems.
Presiding: MD Moran
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 202.
Tanking up: Drought, disturbance, and structure of Sarracenia food webs.
Gotelli, Nicholas*,1, Ellison, Aaron2, 1 University of Vermont, Burlington, Vermont2 Harvard Forest, Petersham, Massachusetts
ABSTRACT- Food webs in rainwater-filled pitchers of the carnivorous plant Sarracenia purpurea are a model system for investigating how disturbance regulates food web structure. This food web is supported by a base of insect prey, and includes prey-shredding midge larvae; detritivorous protozoa and bacteria; omnivorous rotifers, mites, and mosquito larvae; and top-predator sarcophagid larvae. In an ecological press experiment, we disturbed this system by altering water quantity in Sarracenia leaves in a Vermont bog and observing changes in food web structure. During a single field season, one of five manipulations was applied semi-weekly to all leaves of each experimental plant: 1) unmanipulated controls; 2) pitcher water and food web removal; 3) food web removal; 4) pitcher water addition; 5) pitcher water addition and food web removal. Conventional ANOVA revealed that individual taxa responded idiosyncratically to water quantity, although some taxa responded more to variation in leaf age and prey availability than to experimental treatments. Path analysis was used to test simple colonization models based on water volume or prey resources, versus models that incorporated known trophic relationships of the food web. Models without trophic structure fit the data poorly. The best-fitting model was a mixed trophic model that included both top-down and bottom-up effects. Although habitat volume and basal prey resources have important effects, trophic interactions account for more of the variation in food web structure and abundance of individual taxa.
Key words: Sarracenia, disturbance, food web, path analysis