The effects of group size on per capita ingestion in flatworms

CASH, KEVIN J.; Wrona, Frederick J.; SCRIMGEOUR, GARRY J.

The effects of group size on per capita ingestion in flatworms

1995

CASH, KEVIN J. | Wrona, Frederick J. | SCRIMGEOUR, GARRY J.

1. We evaluated the effect of group size on the per capita ingestion rates of three species of flatworm, two of which actively group with conspecifics (Dugesia tigrina, D, dorotocephala) and employ mucus to capture prey, and a third species (Mesostoma ehrenbergii) that does not actively group but does use mucus to capture prey. 2. As flatworm group size increased, daily per capita ingestion first increased and then decreased for D. tigrina and D. dorotocephala. In the case of D. tigrina this pattern was observed even at low predator densities. Ingestion rates of M. ehrenbergii were largely unaffected by group size. 3. Results suggest that the observed changes in per capita ingestion rates with changes in group size previously reported for D. tigrina are related to their tendency for active grouping and are not directly a consequence of prey capture technique or experimental design. 4. We argue that freshwater triclads in general, and D. tigrina in particular, represent an ideal model system for the development and testing of group foraging theory.

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