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Communication at the NABS Annual meeting, Keystone, 2000
(17) FISH MEDIATED ALTERATION OF INVERTEBRATE COMMUNITY SIZE DISTRIBUTIONS IN TWO PRAIRIE WETLANDS.
K.D. Zimmer1, M.A. Hanson2, M.G. Butler1, and W.G. Duffy3. 1Department of Zoology, North Dakota State University, Fargo, ND 58105, 2Wetland Wildlife and Populations Research Group, Minnesota Department of Natural Resources, Bemidji, MN 56601, 3California Cooperative Fisheries Research Unit, Humboldt State University, Arcata, CA 95521
Numerous studies have assessed impacts of fish predation on the abundance and biomass of individual invertebrate taxonomic groups, but relatively few studies have examined impacts of fish on the size structure of an entire invertebrate community. We compared size distributions of aquatic invertebrates in two prairie wetlands; one supporting a population of fathead minnows and the other fishless. Both wetlands were sampled in three depth zones on three dates, allowing assessment of temporal and spatial change. We determined biomass of aquatic invertebrates in 18 log2 weight classes, and used these data to develop normalized size-spectra (NSS). Invertebrate biomass was higher in all size classes, and present in larger size classes, in the fishless wetland, indicating minnow predation was not purely size-selective, but affected a wide spectrum of invertebrate sizes. Intercepts of NSS were significantly different between wetlands but slopes generally were not, indicating a strong impact of minnow predation on standing-stock biomass but a much weaker impact on the size structure of the invertebrate community. Our results indicate invertebrate communities in prairie wetlands can maintain relatively consistent size structures in spite of strong predation pressure, and reduced biomass and altered taxonomic composition are the most prominent effects of minnow predation.
Presented at 1:00 PM on Monday, May 29, 2000 in Wetlands and Lentic Ecology I
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