7026

• UCREFRP Catalog Number: 7026
• Author: Deacon, J. E. and W. L. Minckley
• Title: Desert Fishes
• USFW Year: 1974
• USFW - Doc Type: Desert Biology
• Copyright Material: YES

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434

JAMES E. DEACON AND W. L MINCKLEY

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1963), and in the main seems the most important single variable. This
understanding resulted in large part from early studies by Shelford
(1911a,b) on ecological succession, in which he emphasized the physio-
graphic influences in strcams as being far more important than biotic fac-
tors (Allee et aI., 1949). Geologic maturation of strcams was considered
as a successional phenomenon, followed by succession of the fish fauna
at a given point from those of swift headwater situations to species with
proclivities and morphologies more adapted to downstream or lentic situa-
tions, Such relationships have been demonstrated throughout the world
where fishes inhabit streams.
Figure 6 outlines the actual or generalized distributions of fishes in a
number of regions or stream systems and illustrates correlations between
fish morphology and habitat features of different stream segments. This
correlation cuts across taxonomic groupings, in most part, and serves to
illustrate the close ties between body shape in fishes and the environments
in which they live. That the correlative factor in such situations is current
(or gradient) may easily be demonstrated by examining unusual streams
which flow through flat lands in their headwaters, then enter a section of
higher gradient in their lower reaches;, the longitudinal distribution of fishes
is similarly reversed (Larimore et ai., 1952). IQ Aravaipa Creek, Arizona,
a high-gradient area is sandwiched between two low gradient sections.
Headwater fishes occur mostly in the middle reach of that stream (Barber
and Minckley, 1966). In fact, the simple presence of an arca of swift water
between pools-a riffle-provides living space for headwater fishes in the
midst of lakclike conditions.
Careful examination of shorelines of larger rivers, as opposed to eddies
along the current of the main channel, or the swift, central part, reveal
similar current-related habitat preferences. In well-watered zones, or in
large, persistently flowing desert rivers, a tremendous diversity of species
may exist within this complex type of environment. In other places, a
group may diversify into a number of niches or habitats.
Segregation of a group into differing regimes of current (or current-
related habitats) is remarkably developed in cyprinoid fishes of the Colo-
rado River basin of western North America. The swift-water minnows and
suckers of that system display some of the most bizarre morphological
adaptations to the constant stress of current (and likely suspended solids)
that are known in any river in the world (Hubbs. 1940, 1941a),

In more obvious adaptation ., . the fish tend to be larger and much more
stream-lined . . . , with more terete bodies. sharper entering wedges and.
particularly, with much slenderer caudal peduncles and longer and more
. falcate fins; and often with more rays in one or more fins or with smaller
scales (which provide a smoother surface) (Hubbs, 194Ia).

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