MEPS 157:247-259 (1997)  -  doi:10.3354/meps157247

Prey switching by Acartia clausi: experimental evidence and implications of intraguild predation assessed by a model

Ingrid Gismervik1,*, Tom Andersen2

1Section of Marine Zoology and Chemistry, University of Oslo, PO Box 1064 Blindern, N-0316 Oslo, Norway
2Section of Marine Botany, University of Oslo, PO Box 1069 Blindern, N-0316 Oslo, Norway

Switching between algal (Thalassiosira weissflogii)and ciliate (Strobilidium undinum) food by the marine copepod Acartia clausi was investigated in the laboratory by short incubation experiments with 14C-labeled prey. A. clausi displayed a Holling type 3 functional response (which differed significantly from a type 2 response, p < 0.05) for ciliates when there was a constant abundance of algae present, and likewise for algae when there was a constant abundance of ciliates present. The results were implemented in a mathematical model to investigate the effect of different functional responses on a simple food web comprised of nutrient, algae, ciliates and copepods. In the model, ciliates and copepods competed for resources (algae) and ciliates were also prey for copepods. This blend of predation and competition among copepods and ciliates corresponds to intraguild predation as defined by Polis & Holt (1992; Trends Ecol Evol 7:151-154). Stable solutions with all state variables present were found over a range of nutrient concentrations when the copepods displayed type 3 functional responses. On the contrary, when copepods displayed type 2 responses, such stable solutions were only found at very low input nutrient concentrations. Coexistence of ciliates and copepods further required that ciliates had a lower threshold prey concentration for positive net growth than copepods.

Prey switching · Acartia clausi · Ciliates · Copepods · Algae · Model · Intraguild predation · Stability · Coexistence

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