Dissertation Research: Algal and Zooplankton Community Responses to Piscivory: Mediation Through Alternate Planktivore Types

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One of the most visible symptoms of eutrophication is high phytoplankton standing crop. Recently, investigators have hypothesized that by increasing piscivorous fish densities in lakes, planktivorous fish abundance should be made to decline, leading to higher zooplankton biomass or altered species composition and thus indirectly to lower phytoplankton standing crop. Piscivorous fish are limited in the maximum size of prey they can ingest by the dimensions of their mouths. Because several studies have shown that this "gape limitation" can be very important in influencing interactions between piscivores and their prey, there should be differential effects of piscivores on populations of prey that differ in body shape. This differential predation may in turn influence the degree of piscivore-mediated cascading trophic effects on zooplankton and phytoplankton. Laboratory experiments will examine prey election by piscivorous largemouth bass (Micropterus salmoides) for two species of planktivores representing extremes in general body type: fathead minnows (Pimephales promelas), soft-rayed and shallow-bodied and bluegills (Lepomis macrochirus), hard-spined and deep bodied. A long-term pond experiment using 20 experimental ponds will also examine largemouth bass-fathead minnow and largemouth bass-bluegill interactions and their cascading effects on zooplankton and phytoplankton. The outcome of these experiments will test ecological theory and has immediate applied value in lake management.