Effects of predator confusion on functional responses.

Jeschke, Jonathan M. and Tollrian, Ralph (2005) Effects of predator confusion on functional responses. Oikos, 111 (3). pp. 547-555. ISSN 0030-1299

Abstract

When confronted with a swarm of their prey, many predators become confused and are less successful in their attacks. To shed light on the ecological, ethological and evolutionary consequences of predator confusion, we here investigate its effects on predator functional responses. We develop the first functional response model that considers confusion and compare it (1) qualitatively as well as (2) quantitatively to empirical data from two predator–prey systems, Aeshna cyanea (Odonata)–Daphnia magna (Crustacea) and Chaoborus obscuripes (Diptera)–Daphnia obtusa. (1) The qualitative comparisons show that, contrary to common belief, confusion does not necessarily lead to a dome-shaped functional response. The response can alternatively remain qualitatively unchanged and be affected only quantitatively. A non-dome-shaped response is thus no indication for the absence of predator confusion. The same is true for other swarming effects reducing foraging success, such as early warning of approaching predators. Our results hence question studies that have equated the absence of a dome-shaped response with the absence of a swarming effect. Our results also resolve the apparent paradox that swarming effects are quite common while dome-shaped functional responses are rather uncommon. (2) There is a good quantitative match between a parameterized version of our model and the empirically measured functional response in the Chaoborus-Daphnia system, suggesting that all crucial factors in this system are captured by the model.