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<br />OF NATURALISTS
<br />President-Elect
<br />AN (Ornithology)
<br />till SFATF I1NIVFRSI'I V
<br />S7-1. "TX 78412
<br />Treasurer
<br />LICKS (Vertebrate Systemattr
<br />DLIFE AND FISHERIES SCII"Vt t,
<br />\I V.
<br />TION, TX 77843
<br />Secretary
<br />GHEE (MUSettm SCience)
<br />RGIA
<br />LW2
<br />to Editor, Invertebrates
<br />rTON
<br />.OGY
<br />'.TAN UNIVF,RSI FV
<br />. TX 76129
<br />ciate Editor, Botany
<br />(Plant Taxonomy)
<br />.OGY
<br />ERMTY
<br />18
<br />ciale Editor, Botany
<br />KEN (Plant Ecology)
<br />IFE SCIENCES
<br />,F TEXAS
<br />. Tx 78285
<br />daertising Editor
<br />;s (Marnmalogy)
<br />OGY
<br />F NEW MEXICO
<br />E. NM 87131
<br />Class of 1988
<br />.TTHEWS (Ichthyology)
<br />,HOMA BIOL. STA YION
<br />73439
<br />Ecology, Systematics,
<br />MEXICO
<br />E.NM 87191
<br />Class of 1989
<br />a (Herpetology)
<br />I1rNITY COLLEGE.
<br />998
<br />LAY (Herpetology)
<br />F UNIV.
<br />92
<br />id animals, living and lo..,.
<br />to aid in the scientific a, i,
<br />field trips, and publishr, I i
<br />)ersons interested in naUn.,;
<br />FURALIST, are 520 !,,j y"
<br />A 880 for institutional (tit
<br />)ciation of Naturalists and
<br />,ent to: Steven W, Ke!srh. !r:
<br />tion, TX 77893. This pmor,
<br />tern Association of ?:arm,,
<br />'he Southwestern AAssrx rain„
<br />zM University, Colle,q, I,,-
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<br />
<br />1'ftF; SOUTHWESTERN NATURALIST 30(2):173-187 MAY 31, 1985
<br />PREDATION AND SPECIES REPLACEMENT IN
<br />AMERICAN SOUTHWESTERN FISHES:
<br />A CASE STUDY
<br />GARY K. MEFFE
<br />AssrtteCT.-Declines in distribution and abundance of native fishes of the American Southwest
<br />ytv been noted for decades, but mechanisms leading to these losses are unclear. The Sonoran
<br />pprninnow (Poecitiopsis occidentalis) was studied to determine mechanisms leading to local
<br />ptirpation, as a model of southwestern fish extinctions. Although habitat destruction is the cause
<br />-4teverat population losses, interactions with introduced mosquitofish (Gambusia affinis) are
<br />X?punsible for reduction of topminnows through much of their native range. A series of
<br />oratory and field experiments indicated that predation of juvenile topminnows by
<br />,*quitofish is a major factor in decline of the species- For lack of evidence, introduced parasites
<br />T diseases, hybridization, physiological stress, and resource competition are all dismissed as
<br />ble mechanisms of extirpation.
<br />Local extinction of native species is a common result of introduction of
<br />antic organisms, and man-induced range extensions are a major threat to
<br />integrity of natural communities (Elton, 1958). Despite potentially
<br />trous effects of introduced fishes on native communities (e.g., Miller,
<br />l; Zaret and Paine, 1973), little is known of mechanisms by which
<br />juruders replace natives. Although hypotheses such as competition,
<br />ptedation, and habitat alteration abound, few have been tested. Here, I
<br />Kport an experimental analysis of mechanisms involved in replacement of
<br />& native Sonoran Desert fish by a non-native species, and discuss losses of
<br />jeer southwestern fishes via exotics.
<br />The Sonoran topminnow, Poeciliopsis occidentalis (Baird and Girard), is
<br />mall (<50 mm) poeciliid fish native to the Gila River drainage of
<br />?ttthern Arizona and several major drainages in northwestern mainland
<br />Jpdco (Rosen and Bailey, 1963; Hendrickson et al., 1981). It formerly
<br />rred in most aquatic habitats throughout this region, including stream
<br />tgms, springs, and marshes. In the past four decades, distribution of P.
<br />entalis has narrowed to the extent that it now occurs in the United
<br />only in a few isolated streams, springs, or segments of creeks in
<br />ern Arizona, and is listed as endangered (U.S. Department of the
<br />b ior, 1980). Various aspects of Sonoran topminnow life history are
<br />nsively documented elsewhere (Minckley, 1973; Schoenherr, 1974, 1977,
<br />1; Constantz, 1974, 1975, 1979, 1980; Minckley et A., 1977; Gerking and
<br />tz, 1980; Meffe et al., 1983).
<br />e mosquitofish, Gambusia affinis (Baird and Girard), is a poeciliid
<br />e to temperate and semi-tropical regions of the eastern and central
<br />ed States (Rosen and Bailey, 1963) and is widely introduced through
<br />h of the world. First brought into Arizona about 1926 for mosquito
<br />of (Miller and Lowe, 1964), it is presently ubiquitous and has replaced
<br />Sonoran topminnow throughout much of its former range (reviewed by
<br />1W et A., 1983). On a local scale, replacement occurs from four months
<br />i df
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