FEEDING VARIABILITY AMONG INDIVIDUAL AQUATIC PREDATORS IN EXPERIMENTAL CHANNELS

Experiments were conducted in experimental channels to study feeding v ariability through time and between conspecific individuals of four sp ecies of lotic predators. Large and small Rhyacophila dorsalis (Tricho ptera: Rhyacophilidae) were given black fly larvae, mainly Simulium or natum (Diptera: Simuliidae) of two size classes during laboratory feed ing trials lasting up to 5 days. Acroneuria lycorias (Plecoptera: Perl idae) were also given black fly larvae (Prosimulium fuscum, S. venustu m) during 11-day laboratory feeding trials. Paragnetina media (Perlida e) and Isoperla signata (Plecoptera: Perlodidae), were supplied with a mixed prey assemblage of black fly larvae and mayfly nymphs, Baetis f lavistriga (Ephemeroptera: Baetidae), and Epeorus vitrea (Heptageniida e), for 9 days in field experiments. There was significant variability in the consumption of prey among individuals of R. dorsalis, this bei ng true for both large and small predators. Significant among-predator and day-to-day feeding variability also occured with A. lycorias, P. media, and I. signata. Our experiments showed that there are significa nt differences in prey consumption among individual predators within a given species, and these differences need to be considered when plann ing, and interpreting, future studies on predator - prey interactions, particularly those conducted in experimental streams.