Feeding efficiency of Chaoborus flavicans (Insecta, Diptera) under turbulent conditions
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PRIMARY RESEARCH PAPER
Feeding efficiency of Chaoborus flavicans (Insecta, Diptera) under turbulent conditions Laura Ha¨rko¨nen • Zeynep Pekcan-Hekim Noora Helle´n • Jukka Horppila
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Received: 30 November 2012 / Revised: 4 August 2013 / Accepted: 18 August 2013 / Published online: 29 August 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract Turbulence can affect predator–prey interactions. The effect of turbulence on the feeding efficiency of an ambush predator was tested with laboratory experiments. The experiments were conducted in 100-L aquaria in which ten individuals of fourth instar Chaoborus flavicans larvae were placed as predators. Two prey densities (3 and 10 ind. of Daphnia pulex L-1) and two durations (30 and 120 min) were tested in a nonturbulent treatment and five different turbulence levels [average root-mean-square (RMS) velocities ranging from 0 to 7.3 cm s-1, corresponding dissipation rates from 7.2 9 10-7 to 1.3 9 10-3 m2 s-3]. We hypothesized that the feeding rate of C. flavicans would be enhanced by turbulence due to increasing encounter rates up to a turbulence level above which a disturbance in post-encounter processes would lead to reduced feeding efficiency. However, the results showed no significant increase in the feeding rate of C. flavicans at intermediate turbulence. At high turbulence we found the expected significant negative response in the feeding rate of Chaoborus larvae. The feeding rate declined below the rates at nonturbulent and intermediate turbulence
Handling editor: Karl E. Havens L. Ha¨rko¨nen (&) Z. Pekcan-Hekim N. Helle´n J. Horppila Department of Environmental Sciences, University of Helsinki, P.O. Box 65, 00014 Helsinki, Finland e-mail: [email protected]
conditions as the average RMS velocity exceeded 3.1 cm s-1 (dissipation rate 9.9 9 10-5 m2 s-3, respectively). Keywords Turbulence Planktonic invertebrate Ambush predator Chaoborus flavicans Feeding rate Daphnia pulex
Introduction Predation is one of the major forces influencing population dynamics in freshwater ecosystems (Zaret, 1980). Zooplankton communities in lakes are regulated by both vertebrate and invertebrate predators. Juvenile and adult stages of planktivorous fish prey selectively on large zooplankton, commonly resulting in a zooplankton community dominated by small species (Brooks & Dodson, 1965; Unger & Lewis, 1983). Due to their relatively high abundance, aquatic invertebrates also have a substantial influence on zooplankton populations (Dodson, 1974). Invertebrate predators are able to affect significantly the population abundance of their prey and possibly even the species composition of the community by feeding selectively among zooplankton (Allan, 1973; von Ende, 1979; Liljendahl-Nurminen et al., 2003). Most fish are visual feeders, whereas many invertebrate predators are tactile predators that detect their prey by mechanoand chemoreception. Hence, invertebrate predators have an advantage over fish in circumstances with low
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visibility; at high ino
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