Document: JON-3-56-12

Predator functional response: Discriminating between handling and digesting prey.

JESCHKE, J.M.* ¹, M.KOPP ² and R.TOLLRIAN ¹

Ludwig-Maximilians-Universität, Karlstr. München D-80333 Germany ¹
Max-Planck-Institut für Limnologie, Plön D-24302 Germany ²

Abstract:
We present a mechanistic functional response model that realistically incorporates handling (that is attacking and eating prey) and digesting prey, thereby filling a gap in present functional response theory. We treat digestion as a background process which does not prevent further foraging activities (searching and handling). Instead, the hunger level is assumed to determine the predator's probability of attack. Additionally, the model accounts for time wasted through unsuccessful attacks. Since a main assumption of our model is that the predator's hunger is in a steady state, we term our model the steady state satiation (= SSS) equation. It can, for example, be used to calculate effects of changing predator or prey characteristics (e.g. defenses) on predation rate. The SSS equation reveals a new formula for the asymptotic maximum predation rate (i.e. asymptotic maximum number of prey eaten per unit time, for an infinite prey density). According to this formula, maximum predation rate is defined not by the sum of the time spent for handling and digesting prey, but solely by the larger of these two terms. As a consequence, predators can be categorized into two types: handling-limited predators (maximum predation rate is limited by handling time, e.g. the heterotrophic flagellate Ochromonas) and digestion-limited predators (maximum predation rate is limited by digestion time, e.g. the oystercatcher, Haematopus ostralegus). Based on available data, we expect that most predators are digestion-limited.

Keywords: Digestion-limited predators, functional response, handling-limited predators, predators, prey, SSS equation

This abstract is being presented at: 4:45 PM in session:
Oral Session #63: Evolutionary Ecology.