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<br /> <br />8 <br /> <br />OVERVIEW OF RIVER-FLOODPLAIN ECOLOGY IN THE UPPER MISSISSIPPI RIVER BASIN <br /> <br />Aquatic and semi-aquatic invertebrates can be sepa- <br />rated into functional groups adapted to living in specific <br />habitats. Benthic invertebrate ecology is not well known in <br />main channels. but invertebrates found there are both ana- <br />tomically and behaviorally adapted to life in high-flow <br />shifting-sand environments (Sol uk and Craig. 1988. 1990). <br />Low-flow microhabitats exist in the boundary layer around <br />rocks and snags, and some insects have adapted mecha- <br />nisms for survival in swift-flowing habitats (Cummins, <br />1972). <br />Main channel border habitats experience lower current <br />velocity, and substrates are more stable; burrowing inverte- <br />brate communities dominate the benthic fauna (Hexagenia <br />mayflies. unionid mussels. fingernail clams) (Anderson and <br />Day. 1986; Elstad. 1986), These animals filter organic mat- <br />ter from the water column and are frequently found in high <br />concentrations near zones of high aquatic or floodplain <br />plant production (Anderson and Day. 1986: Grubaugh and <br />others. 1986: Grubaugh and Anderson. 1989), Benthic graz- <br />ers and detritivores are present as well. If vegetated, channel <br />borders support communities similar to those in backwaters. <br />Snags and other hard substrates in flowing habitats support <br />high densities of net-building filter feeders (caddisflies) <br />(Seagle and others, 1986). <br />Side channel invertebrate communities vary in <br />response to flow, sediment type, and vegetation. Inverte- <br />brate community structure is similar to that of main channel <br />and channel border habitats, <br />Backwater invertebrate communities range from very <br />diverse to very sparse in terms of species composition. In <br />open backwater areas. benthic filter feeders may be present. <br />but detritivores and algal grazers (chironomids. zooplank- <br />ton) typically dominate (LTRMP. unpub, data). When vege- <br />tation is present, diversity increases, and the community <br />consists of grazers, detritivores, algal scrapers (herbivores), <br />and predators (Chilton, 1990), There are many aquatic and <br />semi-aquatic invertebrates (corixids, various beetles, and <br />zooplankton) that have adaptations for rapid colonization <br />and exploitation of ephemeral habitats (Cummins. 1972). <br />such as those created by flooding, Some species have <br />evolved mechanisms for surviving dry periods, thus allow- <br />ing them to flourish when favorable environmental condi- <br />tions do occur (Cummins, 1972), <br /> <br />FISHES <br /> <br />Many fishes are anatomically. physiologically. and <br />behaviorally adapted to exploit specific habitats (Pflieger. <br />1975; Pollard and others. 1983: Wien. 1991; Holland- <br />Bartells and others. 1993), but most are also opportunistic <br />and take advantage of resources as they become available <br />(Welcomme. 1979; Junk and others. 1989; Bayley. 1991). <br />Others may be highly migratory, such as paddlefish, Ameri- <br />can eel, and skipjack herring (Pflieger. 1975). The most <br /> <br />applicable generalization for UMR fishes divides species <br />into lacustrine (lentic) and riverine (lotic) groups, <br />Lacustrine fishes are adapted to the slow-flowing or <br />still waters found in backwaters, sloughs. channel borders, <br />and dike fields, These are primarily nest-building species <br />that guard their young, They are generally highly opportu- <br />nistic feeders and target invertebrate and fish prey. depend- <br />ing on their mouth gape and the prey availability. <br />Riverine fishes are adapted to the flowing conditions <br />of main channel. channel border. and side channel habitats. <br />They have behavioral adaptations such as benthic feeding, <br />and anatomical adaptations such as fusiform (streamlined) <br />morphology that allow them to survive in the environment <br />of the main channel. They display a variety of spawning <br />requirements that range from broadcast spawning in the <br />water column (freshwater drum) to dependence on flooded <br />vegetation (buffalo and pike). Some species (benthic feed_ <br />ers) are opportunistic (common carp), while others are pri- <br />marily piscivores (flathead catfish), Fishes that are abundant <br />in all habitats are usually generalist feeders. <br /> <br />AMPHlBtANS AND REPTILES <br /> <br />Because the river-floodplain ecosystem offers great <br />habitat diversity. herpetofauna are abundant in the UMR, <br />Besides regional differences, considerable differences in <br />species composition occur among different habitats of the <br />UMR (1. Tucker. personal commun,. 1993), Few reptiles <br />and amphibians are dependent on the open river itself for <br />survival. Twenty-eight of III species (Conant and Collins, <br />1991) use main channel or side channel habitats, Alligator <br />snapping turtles and map turtles are dependent on these hab- <br />itats (Smith. 1961), Most other aquatic species require tribu- <br />tary mouth. marsh. or bank-side habitat. Terrestrial species <br />are found in floodplain forest and prairie habitats, Forest <br />species (59) are concentrated in the middle river reach. and <br />mesic and sand prairie species (39) are concentrated along <br />the Illinois River and in the lower floodplain reach, <br /> <br />BIRDS <br /> <br />Because the Illinois and Mississippi Rivers support <br />major migratory flyways, avian fauna is very diverse in the <br />river-floodplain environment. The migrants usually use <br />river resources once on the northern migration and again on <br />the southern migration; a few individuals of many species <br />remain scattered throughout the basin (Bellrose. 1980), <br />Waterfowl are perhaps the best known and fall into three <br />major groups. Diving ducks feed on soft substrate inverte- <br />brates and tubers in channel borders and deep backwaters. <br />Dabbling ducks use shallow backwater and floodplain <br />vegetative resources and epiphytic invertebrates. Geese usu- <br />ally feed on vegetation in the floodplain. Reproduction <br />