Role of fish predation in the distribution of Chaoborus americanus and Leptodora kindtii.

Abstract

It has been observed that Chaoborus americanus and Leptodora kindtii do not coexist in the zooplankton communities of Bryant's Bog and Douglas Lake. C. americanus is found in Bryant's Bog (a fishless environment), while L. kindtii is found in Douglas Lake (containing fish). This study looks at the possible role of fish predation in the observed species distribution. Perca flavescens (yellow perch) from Douglas Lake were fed individual C. americanus and then individual L. kindtii to obtain reaction times. The perch were then fed the two species at the same time to determine the existence of any species preference. Trials were also run using zooplankton stained with rhodamine to see how color affected prey selection by the perch. Results show that C. americanus was significantly selected over L. kindtii in both the stained and unstained trials, although the percentage of L. kindtii selected more than doubled in the trials done with the stained zooplankton. Thus, differential fish predation (at least in part due to color) may account for the absence of C. americanus from Douglas Lake.