The realized food niches of three species of stream‐dwelling triclads (Turbellaria)

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Abstract
SUMMARY. 1. The diet of Phagocata vitta, Crenobia alpina and Polycelis felina in a Welsh stream was examined, using a serologicat technique, at monthly intervals over 18 months.2. For each triclad species, dietary composition changed little with time or increasing body size, and overall feeding intensity was greatest in summer and least in winter.3. Alt species fed most heavily on oligochaetes, chironomids and Gammarus. Phagocata vitta fed lightly on Plecoptera, Trichoptera and Ephemeroptera whilst the other two triclad species fed substantially on the first two of these prey categories.4. Food niche breadth indices indicated a wide diet for all species with some specialization in some months. Electivity indices showed positive electivity for oligochaetes and chironomids by all species and for Plecoptera by C. alpina and P. felina.5. Diets overlapped and none had a food refuge: therefore the potential for interspecific competition for food exists.