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<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 />
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