PARENT SESSION
Wednesday, August 9, 8:00-11:50 am
OOS 8 - When does fear matter? A road map to the implications of trait-mediated effects to ecology
Ballroom D, Ballroom Level, Cook Convention Center
Organized by: EL Preisser (preisser@psis.umass.edu), G Trussell, and E Werner

This session synthesizes mathematical theory, conceptual work, and empirical research to explore the factors influencing the relative importance of trait- and density-mediated effects in ecological communities.

The dynamics of food web models containing dynamic traits; implications for defining and measuring interspecific interactions.

Abrams, Peter^*,1, ¹ University of Toronto, Toronto, ON, Canada

ABSTRACT- It is likely that a large fraction of species in most natural communities experience interspecific interactions that are shaped by phenotypic plasticity, including adaptive behavior. In particular, predator-prey interactions are likely to be shaped by adaptively variable foraging in the predator and adaptively variable defense in the prey. I use a series of mathematical models to address the measurement of the impact of the prey's behavior on the interaction. These models include adaptive variation in foraging effort and diet choice on the part of the predator and also include adaptive variation in defense on the part of the prey. Several different potential costs of each of these behaviors are analyzed. The rules that govern the rates of change of behaviors are shown to have a significant impact on interaction strength for a given set of assumptions regarding the costs of the traits. I also analyze the potential for empirical measurement of the contribution of the prey's defensive behavior to such an interaction. There have been many empirical estimates of the impact of prey defense on predator-prey interactions, and a large fraction of these have been carried out using functionally disabled predators. I show that this methodology is likely to lead to overestimates of the impact of prey behavior on prey fitness and is unsuitable for measuring the impact of prey behavior on predator fitness. I also discuss the definition of the term 'trait mediated interaction', and argue that such a term should not be used to describe the impact of prey defense on a predator-prey interaction.

Key words: interaction strength, trait mediated indirect interaction, predator-prey interaction