PARENT SESSION
Contributed Oral Session 116: Predator - Prey Ecology: Modeling
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 518 C, Level 5, Palais des congrès de Montréal

Are the prey- and ratio-dependent functional responses really extremes along a continuum of predator interference?

Jensen, Christopher^*,1, ¹ Stony Brook University, Stony Brook, NY, United States

ABSTRACT- The prey-dependent functional response of Holling (1959) has remained the 'standard' for predator-prey models since it was popularized by Rozenzweig and MacArthur (1963). This functional response form has been criticized because it ignores the potential effects of predator interference: experiments have consistently demonstrated that predator density affects consumption rate. If interference is important, how should predator density be incorporated into the functional response? One answer to this question was provided by Arditi and Ginzburg (1989), who proposed the ratio-dependent functional response. Since its introduction, ratio dependence has been considered in opposition to prey dependence, sparking a large debate in the theoretical literature. In particular, the review of Abrams and Ginzburg (2000) suggested that the prey- and ratio-dependent forms exist as two ends of a continuum of predator interference. Using the predator-dependent forms of Hassell-Varley (1969) and Beddington-DeAngelis (1975), both of which allow for variable predator interference, I explore the nature of this continuum via numerical simulation. I show that the choice of predator-dependent form has a strong effect on model outcomes: while the functional response of Hassell-Varley bridges the behaviors of the prey- and ratio-dependent models across a continuum of interference, the Beddington-DeAngelis form does not. At low prey growth rates (r) and intermediate levels of predator interference, Hassell-Varley produces dual extinction. Such dual extinction is absent when Beddington-DeAngelis is employed; in fact, at very low levels of interference dual extinction is all but eliminated as a potential outcome. I demonstrate how a set of simple laboratory experiments have the potential to distinguish between the Beddington-DeAngelis and Hassell-Varley functional responses.

Key words: Functional Response, Predator Interference, Microcosms, Paramecium-Didinium