Publication Date


Document Type


First Advisor

Ende, Carl von

Degree Name

B.S. (Bachelor of Science)

Legacy Department

Department of Biological Sciences


The purpose of this project was to evaluate the effect of predator group size on per capita ingestion rates of the flatworm Dugesia tigrina, and to determine whether an optimum group size exists. In previous experiements performes by Cash et al. (1993,1995), it was determined that when Dugesia was fed Daphnia and mosquito larvae, per capita ingestion rates were higher in predator groups of four and eight. My project was designed to determine if the same pattern would be found if the flatworms were given isopods (Caecidotea sp.,) to prey upon, which are benthic organisms. To accomplish this, flatworms were maintained in groups of one, two , four, eight, ten, and sixteen, and were fed a constant ratio of three isopods per predator. Each experiment was run for five days, counting and replacing eaten prey daily. A total of six experiments were performed, three of which included a mesh screening in the bottom of the dishes. Per capita ingestion rates were determined and analyzed. The results showed no significant difference in per capita ingestion rates between group sizes. However, there was a significant overall decrease in per capita rates among the flatworms in the dishes containing screen compared to those without the screen. It is hypothesized that the screen enabled the isopods to more easily escape predation by the flatworms. It is thought that, in addition to a food source, this may be one reason that isopods in natural environments are found on the undersides of dead leaves and vegetation.


Includes bibliographical references.


14 unnumbered pages




Northern Illinois University

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