Foraging Mode Switches in the Golden Shiner (Notemigonus crysoleucas)

Abstract

Golden shiners (Notemigonus crysoleucas) use two distinct foraging modes when feeding on zooplankton. Shiners particulate-feed on large cladocerans, visually locating and attacking individual prey items. Shiners also pump filter-feed on high densities of small zooplankton, using no apparent visual cues to detect prey. Particulate-feeding and filter-feeding functional response curves were determined from laboratory experiments. Particulate-feeding rates on Daphnia pulex increased with shiner size, but filter-feeding rates on Bosmina decreased with shiner size. Experiments with both prey types present simultaneously revealed that shiners can switch between foraging modes on a short time scale which increases their total foraging return by filter-feeding on Bosmina in between Daphnia encounters. This behavioral flexibility has consequences for both fish and zooplankton community structure in winterkill lakes. The ability to switch feeding modes on a short time scale allows shiners to exist in lakes that are dominated by small zooplankton yet still provides a mechanism to effectively remove large cladocerans when they are encountered.