PREDATOR AVOIDANCE AND COMMUNITY STRUCTURE - INTERACTIONS AMONG PISCIVORES, PLANKTIVORES, AND PLANKTON

Small bluegills Lepomis macrochirus shift their habitat use in the presence of their predator, largemouth bass Micropterus salmoides. The addition of bass causes small bluegills to make greater use of structured (vegetated) habitats and reduces their use of open (limnetic) habitats. By stocking small bluegills with and without bass, pronounced differences in zooplankton abundance and size structure developed between treatments, with 3 cladocerans (Daphnia, Diaphanosoma, Ceriodaphnia), and the phantom midge Chaoborus, becoming more abundant with bass. These effects of bass were not due to changes in bluegill abundance, as very few bluegills were eaten by the bass, and bluegill densities did not differ between treatments. Bluegills exerted substantial mortality on the zooplankton and cladocerans experienced lower per capita death rates (due to bluegill) in the presence of bass. Results are discussed in light of theory predicting how foragers should deplete prey among habitats that differ in mortality risk. -from Authors