MEPS 317:75-86 (2006)  -  doi:10.3354/meps317075

Behavioural mechanisms underlying functional response of sea stars Asterias vulgaris preying on juvenile sea scallops Placopecten magellanicus

Melisa C. Wong1,*, Myriam A. Barbeau2, Michael Dowd3, K. R. Richard2

1Institute of Marine Sciences, University of North Carolina-Chapel Hill, Morehead City, North Carolina, 28557 USA
2Department of Biology, University of New Brunswick, Fredericton, New Brunswick E3B 1E6, Canada
3Department of Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada

ABSTRACT: The functional response characterises the relationship between prey density and the consumption rate of individual predators. Typically, it is studied by fitting a model to observations of predation rate at different prey densities. The behavioural mechanisms underlying a functional response are not well understood, and estimates of model parameters seldom conform to observations of behaviour. We have developed a mechanistic approach that directly incorporates behavioural observations into characterisation of the functional response. Laboratory experiments were used to record predation rates and observe foraging behaviour of sea stars Asterias vulgaris preying on juvenile sea scallops Placopecten magellanicus at different densities. Experiments were conducted in tanks with no sediment and tanks with sediment. Behavioural data from the experiments were used to calculate parameters of functional response models Th (handling time per prey) and a (rate of successful search). On both substrates, Th remained constant across prey density, while a was density-dependent. An inverse quadratic was used to describe a and was incorporated into a functional response model. Estimates of a were also obtained by fitting the functional response model to the predation rate data using regression analysis. These estimates of a were highly consistent with the estimates calculated from behavioural data. On both substrates, sea stars preying on scallops had a Type III sigmoid-shaped functional response; on sediment, predation rate decreased at high prey densities. Sea star ability to capture attacked prey was probably the mechanism underlying the observed responses. In general, behavioural information can lead to better understanding of observed functional responses.

KEY WORDS: Functional response · Behavioural mechanisms · Rate of successful search · Handling time · Prey density · Sea scallop · Placopecten magellanicus · Sea star · Asterias vulgaris · Sediment

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