The effect of fish predation on community structure in two large freshwater zooplankton, Leptodora kindtii and Chaoborus americanus.

Abstract

The size-efficiency hypothesis of fish predation has dominated the literature on zooplankton community structure for the past several years. Based on this hypothesis, the preference of fish for larger prey will determine zooplankton distribution. Large species will dominate lakes with low levels of vertebrate predation while smaller ones will thrive when fish predation is heavy. We examined the distribution of two large freshwater zooplankton, Leptodora kindtii and Chaoborus americanus in two lakes of northern lower Michigan. Unlike Leptodora, Chaoborus is never found in lakes with fish. We determined that fish preferentially feed on Chaoborus over Leptodora. Since this difference could not be explained on the basis of body size, we examined other factors which might play a role. Body color and movement both appear to be important factors in fish prey selection. As a result of this differential predation, zooplankton distribution and community structure are influence by fish predation, but size is not the determining factor.