SHORT-TERM AND LONG-TERM CONSEQUENCES OF GROUPING AND GROUP FORAGING IN THE FREE-LIVING FLATWORM DUGESIA-TIGRINA

1. We evaluated the short-term effect of group size on the per capita ingestion rates, and the long-term reproductive and fitness consequences of group living in the free-living triclad, Dugesia tigrina. 2. As D. tigrina group size increased, daily per capita ingestion rates first increased and peaked at a group size of approximately four, then decreased until, at larger group sizes. ingestion rates did not differ from those experienced by solitary foragers. 3. The general qualitative pattern of changing per capita ingestion rates with changes in group size was not affected by changes in prey density, prey species or predator size. 4. Long-term experiments indicate that individuals maintained in groups of four produce significantly more and larger asexual fission products than do their solitary counterparts. 5. This study provides the first direct quantitative link between group membership (and its impact on per capita ingestion) and correlates of fitness such as survival and fecundity. 6. 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.