9410

• UCREFRP Catalog Number: 9410
• Author: Wydoski, R. S. and E. J. Wick.
• Title: Ecological Value of Floodplain Habitats to Razorback Suckers in the Upper Colorado River Basin.
• USFW Year: 1998.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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included extremely variable streamflows and high sediment loads. These fishes
evolved together and, more than likely, formed a stable fish community where
competition and predation were balanced. The main natural predator on the
native fishes in the Upper Colorado River Basin was the Colorado squawfish.
The other native species occupied various habitats (i.e., niches) that reduced
competition for food resources.

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Today, the fish fauna in most areas of the Colorado River Basin bears little
resemblance to the fish community that occurred historically. Nonnative fish
species now compose 76% (42 of 55 species) of the fish community in the Upper
Colorado River Basin (Tyus et al. 1982). Since the nonnative fishes did not
evolve with the endangered fishes, mechanisms to balance predation and
competition to allow co-existence have not developed so nonnative fishes
predominate in the present fish community. This change in the fish community
is consistent with ecological theory where species that are more efficient in
capturing and converting food into biomass (i.e., nonnative species) will
persist over other species (i.e., native species) as resources become scarce
(Tilman 1982) .

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III. ECOLOGICAL IMPORTANCE OF FLOODPLAINS

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The importance of the land-water interface to the productivity of lotic
systems has been recognized for over twenty-five years (Allan 1995; Hynes
1970; Hynes 1983; Schlosser 1990, 1991; Ward 1989). However, interpretation
of the complexity of biological responses and importance of geomorphological
or hydrological processes has occurred only recently.

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Historically, the ecological concepts of the river continuum (Vannote et al.
1980) and flood pulse (Junk et al. 1989) applied to the Upper Colorado River
Basin. The river continuum concept applied to the headwaters and high
gradient, restricted meander, canyon reaches while the flood pulse. concept
applied to low gradient, unrestricted reaches that form floodplains in broad
valleys. Lotic systems not only transfer organic matter from upstream reaches
in arid or semi-arid regions (i.e., continuum concept) but also deposit this
material in floodplains where these nutrients aid in high productivity of
invertebrates that periodically transfers food organisms to the main channel
of the river (i.e., flood pulse concept). Most of the productivity in a large
river-floodplain ecosystem occurs in the floodplain and is dependent upon the
duration of inundation and the area of inundation (Junk et al. 1989). With
dam construction, river ecosystems became fragmented (Ward and Stanford 1983,
1995) so that the continuum concept of energy transfer has been greatly
disrupted. Although the flood pulse concept was probably more important to
energy transfer than the continuum concept before Upper Basin rivers were
altered, the flood pulse concept is even more important today to productivity
of the present fragmented river ecosystem where extensive levees continue to
separate much of the floodplain habitat from main channels. The major zone of
productivity in a floodplain is the "moving littoral" (i.e., a shallow zone
that extends from the edge of the waterline to several meters in depth)
because it covers the maximum area of a floodplain for a given flood as it
traverses the floodplain during inundation and draining (Junk et al. 1989).

Floods and floodplains are now understood to be essential components of large
river systems (Bayley 1991; Petts and Maddock 1994; Sedell et al. 1989;
Welcomme 1995). The energy dynamics of large rivers is strongly influenced by
floodplain habitats (Sedell et al. 1989) where productivity is higher than in
river channel habitats (Hynes 1970; Welcomme 1985; Welcomme 1989).
Floodplains provide a greater opportunity for retention and processing of
nutrients and organic matter than main river channels (Sparks 1995). The
spawning strategies of fishes in many tropical and temperate areas are
correlated with the flood pulse that is associated with high productivity in
shallow, flooded areas (Copp 1989; Junk et al. 1989). Ephemeral wetlands in
arid regions (e.g., floodplains, arroyos, and playa lakes) are not included in

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