Biology Reference
In-Depth Information
16.
Alien Species as Agents of
Extirpation and Extinction
“Through gains of exotic species and losses of native ones, the total number
of species world-wide has declined and faunas and floras are losing their
regional distinction.”
—L
OCKWOOD ET AL
. (2000)
The White Mountains of Arizona hold the headwater streams of several
branches of the Salt, Gila, and Little Colorado rivers.These streams were
originally occupied by the Apache trout (
Oncorhynchus apache
). Some of
these streams were first stocked with cutthroat trout (
O. c larki
) in the late
1800s, and many were repeatedly stocked with cutthroat, rainbow (
O.
mykiss
), brook (
Salvelinus fontinalis
), and brown trout (
Salmo trutta
) through
the mid- and late 1900s (Carmichael et al. 1993). The uniqueness of the
Apache trout was recognized in the 1960s, although the species was not
formally described until 1972. Since the 1960s, efforts have been made to
protect White Mountain streams and stock them with hatchery-reared
Apache trout. By then, however, it was apparent that the native Apache
trout population had been severely affected by competition with brown
and brook trout and hybridization with cutthroat and rainbow trout.
Studies were undertaken in 1987-1989 to determine the genetic sta-
tus of trout in the White Mountain area, using allozyme electrophoresis.
A series of genetic markers for Apache, cutthroat, and rainbow trout were
identified, enabling all possible genetic intergrades among these species to
be distinguished. Out of 31 populations sampled, only 11 contained pure
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