Publication Date


Document Type


First Advisor

Ende, Carl von

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences


Fishes--Feeding and feeds; Biotic communities; Aquatic insects


The effects of fish predation on an aquatic insect community were studied in the riffle area of a 3^(rd) order stream in northern Illinois. Two groups of rock-filled wire baskets (25x25x10cm, 0.6cm mesh) were set out on separate dates (5/7 & 5/14/89) and recovered after 3 wks in the stream (Time treatment). Within each group, there were 6 pairs of fish-accessible/fish-exclusion baskets (Fish treatment), the pairing designed to account for spatial variability in the riffle. In addition, a large flooding event occurred between the collection dates, significantly changing the composition of the insect community. Analysis by two-way nested ANOVA revealed higher total abundance (P=.003) and lower H' diversity (P=.05) and a trend toward higher total density (P=.069) of insects in the fish-exclusion baskets and decreased abundance and density after the flood. MANOVA analysis further revealed a Fish effect on chironomids before the flood, when these animals were the predominant taxon in the community, but there was no Fish effect on chironomids after the flood, when chironomid relative abundance was much lower. Conversely, fish had no effect on the abundance of the non-chironomids before the flood but they did significantly depress non-chironomid abundance after the flood. Because the Fish treatments did not differ in terms of abiotic factors the observed results appear to be due to differential fish predation between the treatments. There were abiotic differences between pairs, however, suggesting that experimental designs which take this into account may be required to detect subtle effects of fish predation in streams with significant microhabitat variability. The results of this study suggest that fish can be important structuring agents of lotic insect assemblages when insect communities are reduced. Because the numbers of lotic insects are often at below peak levels due to periodic flooding and mass emergences, fish may have a more important effect than other studies have suggested.


Includes bibliographical references (pages 61-70)


vi, 70 pages




Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type