Temporary intermissions in capturing prey (Daphnia) by planktivorous fish (Rutilusrutilus): Are they due to scramble competition or the need for antipredation vigilance?
Capture rates in planktivorous fish may differ in individuals foraging alone or in a group, and this may result either from the altered risk of predation due to vigilance sharing in the group, or from a difference in the intensity of scramble competition for encountered prey items. Changes in capture frequency and the feeding pattern observed in young roach (Rutilus rutilus) feeding alone and in a group of three on a high density prey (Daphnia), in the presence and in the absence of predator odor, were used to determine which of these two alternate explanations is more likely. Earlier studies revealed that a foraging roach captures Daphnia prey in uninterrupted sequences of captures occurring every 1–3 s. Such multiple captures are separated by intermissions of 10–20 s, with their duration being likely to determine the overall capture rate. An experiment was performed to examine whether feeding in a group of three permits higher capture rates (hypothesis 1), and whether the intermittent foraging pattern is due to the need to invest more time for vigilance when foraging alone (hypothesis 2). Video recordings were made of many series of subsequent prey captures by roach feeding on high Daphnia densities, alone or in a group, and in the presence or absence of predator odor. Analysis of these data revealed that the mean duration of intermissions between bursts of feeding activity was significantly greater in the presence of predator odor, which resulted in a significant decrease in the capture rate. Furthermore, when the roach were feeding in a group, these intermissions were reduced to a greater extent in the presence of predator odor than in its absence, implying that the intermission intervals represent an investment for vigilance as an effective antipredation defense that permits increased food intake regardless of whether or not it is enhanced by the resource or the interference competition.
KeywordsAggregating Antipredation defenses Capture rate Feeding rate Fish impact Handling time Temporal–spatial distribution Vigilance sharing Zooplankton
- Gliwicz, Z. M., 2003. Between Hazards of Starvation and Risk of Predation: The Ecology of Offshore Animals. International Ecology Institute, Oldendorf/Luhe: 379.Google Scholar
- Gliwicz, Z. M. & A. Jachner, 1992. Diel migrations of juvenile fish: a ghost of predation past or present? Archive für Hydrobiologie 124: 385–430.Google Scholar
- Gliwicz, Z. M., P. Dawidowicz, A. Jachner & W. Lampert, 2001. Roach habitat shifts and foraging modified by alarm substance. 2. Reasons for different responses of fish in field and laboratory. Archiv für Hydrobiologie 150: 377–392.Google Scholar
- Isaacson, A. J. & N. J. Westwood, 1971. The significance of gregarious feeding behaviour and adrenal stress in a population of wood-pigeons, Columba palumbus. Journal of Zoology (London) 165: 53–84.Google Scholar
- Krebs, J. R. & N. B. Davies, 1993. An Introduction to Behavioural Ecology, 3rd ed. Blackwell Science, Oxford: 420.Google Scholar
- Krebs, J. R. & N. B. Davies, 1997. Behavioural Ecology: An Evolutionary Approach. Blackwell Science, Oxford: 446.Google Scholar
- Lampert, W. & C. J. Loose, 1992. Plankton towers: bridging the gap between laboratory and field experiments. Archiv fűr Hydrobiologie 126: 53–66.Google Scholar
- Lima, S. L., 1998. Stress and decision making under the risk of predation: developments from behavioral, reproductive, and ecological perspectives. In Møller, A. P., M. Milinski & P. J. B. Slater (eds), Stress and Behavior. Advances in the Study of Behavior, Vol. 27. Academic Press, San Diego: 215–290.Google Scholar
- O’Brien, W. J., 1987. Planktivory by freshwater fish: thrust and parry in the pelagia. In Kerfoot, W. C. & A. Sih (eds), Predation: Direct and Indirect Impacts on Aquatic Communities. University Press of New England, Hanover and London: 5–16.Google Scholar
- Pitcher, T. J., 1986. The function of schooling behaviour in teleosts. In Pitcher, T. J. (ed.), The Behaviour of Teleost Fishes. The John Hopkins University Press, Baltimore, Maryland: 294–337.Google Scholar
- Pitcher, T. J. & J. K. Parrish, 1993. Functions of shoaling behaviour in teleosts. In Pitcher, T. J. (ed.), Behaviour of Teleost Fishes. Chapman & Hall, London: 363–439.Google Scholar
- Rygielska-Szymanska, E., 2009. Size distribution and age structure of a Daphnia population as an effect of size-selective predation by planktivorous fishes. PhD Thesis, University of Warsaw (in Polish, English summary).Google Scholar
- Smith, P. C. & P. R. Evans, 1973. Studies of shorebirds at Lindisfarne, Northumberland. I. Feeding ecology and behaviour of the bar-tailed godwit. Wildfowl 24: I35–I39.Google Scholar