Analysis of the food niche of Glossiphonia complanata (Hirudinoidea: Glossiphoniidae)

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Abstract
The food niche of G. complanata was evaluated in the field using a serological technique. The feeding ecology of the species was similar in the 2 field sites examined, both populations displaying similar trends in prey utilization on a temporal and weight (size-age) basis. Field prey range of G. complanata was determined to consist of Gastropoda, which formed the highest proportion of the diet, followed in decreasing magnitude by Oligochaeta, Chironomidae and Amphipoda, respectively. Feeding activity was lowest in winter and early spring and highest in late spring and summer. The temporal trend in prey utilization (winter to summer) was a continual decrease in Chironomidae and Amphipoda consumption, with a corresponding increase in the proportion of Gastropoda and Oligochaeta utilized. G. complanata partitioned food resources on the basis of weight (size-age) differences. Separation in food niche utilization by the weight classes was a function of a decrease in the proportion of Oligochaeta utilized and an increase in the amount of Chironomidae and Amphipoda consumed with increased predator size. Possible explanations for the observed temporal and weight (size-age) differences in prey utilization are forwarded.