Predator Avoidance and Community Structure: Interactions among Piscivores, Planktivores, and Plankton
1990
Turner, Andrew M. | Mittelbach, Gary George
We present the results of an experiment designed to examine the role predator—avoidance behaviors play in structuring a community. Previous studies have shown that small bluegills (Lepomis macrochirus) shift their habitat use in the presence of their predator, the 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. We hypothesized that these effects of bass on bluegill behaviors should lead to an increase in the abundance and mean size of zooplankton when bass are present. We tested this prediction in two ponds by stocking small bluegills with and without bass. Pronounced differences in zooplankton abundance and size structure developed between treatments, with three cladocerans (Daphnia, Diaphanosoma, and 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. Calculation of bluegill feeding rates shows that the fish exerted substantial mortality on zooplankton and that cladocerans experienced lower per capita death rates (due to bluegill) in the presence of bass. We discuss these results in light of current theory predicting how foragers should deplete prey among habitats that differ in mortality risk.
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