Size-Dependent Diel Foraging Periodicity of a Mayfly Grazer in Streams with and without Fish

Abstract

We tested the hypothesis that predation risk from diurnal fish influences the diel foraging periodicity of the mayfly grazer, Baetis tricaudatus Dodds, in a size-dependent manner by examining habitat use and foraging activity of mayflies in streams with and without these fish predators. In each stream diel habitat use was determined by counting the number of small (3 mm total length) and large (6 mm total length) Baetis larvae foraging on the upper surfaces of replicate, natural cobble during 4-8 sampling periods within a 24-h cycle over three seasons. Additionally, larvae were collected and preserved so that the dial periodicity in gut fullness could be determined