PARENT SESSION
Contributed Oral Session 104: Predator - Prey Ecology: Communities; Defenses
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal

Fear and loathing in a mesocosm: Producing predator-induced defenses in a temporally variable environment.

Schoeppner, Nancy^*,1, Relyea, Rick¹, ¹ University of Pittsburgh, Pittsburgh, PA

ABSTRACT- A major tenet for the evolution of inducible defenses is that organisms must experience variation in predation risk over space or time. While we know that constant predation risk induces profound changes in prey phenotype, we don't know how prey respond to fine-grained variation in predation risk when mean predation risk is held constant. Because predator-induced traits are typically described by a saturating function, Jensen's inequality predicts that phenotypic responses should be less intense when prey experience variable predation risk compared to constant exposure to the same mean level of risk. We examined this question by exposing wood frog tadpoles (Rana sylvatica) to different types of variation in predation risk while holding mean predation risk constant (mg of prey/caged predator/day). Using outdoor mesocosms, we varied the frequency of prey consumption (every 1, 2, 4, or 8 days), the amount of prey consumption (rotating among 200, 400 and 600 mg of prey), and the number of predators doing the consuming (rotating among 0, 2, and 4 caged dragonfly larvae; Anax junius). After measuring tadpole behavior and morphology, we found that all treatments with predators induced strong prey defenses (low activity, deep tails, and short bodies). Quite surprisingly, exposure to a wide range of variation in predation risk had little or no effect on prey traits, suggesting that prey responses are determined by the integration of predation risk rather than by tracking the frequent fluctuations in risk that can occur in nature.

Key words: amphibian, fine-grained variability, inducible defenses, Jensen's inequality