Biology Reference
In-Depth Information
immediately following World War II. This snake caused the loss from Guam of ten
forest bird, three seabird, 1-3 bat, and six lizard species within a span of approxi-
mately 40 years (Savidge, 1987a; Engbring and Fritts, 1988; McCoid, 1991; Rodda
and Fritts, 1992; Fritts and Rodda, 1995, 1998; Rodda et al., 1997, 1999b; Rodda
and Savidge, 2007). Three of the birds and one bat were endemic to Guam and are,
therefore, globally extinct. Two further bird species remain only in captivity, and
most of the native vertebrates remaining on Guam do so at extremely reduced abun-
dances (Rodda and Savidge, 2007), where too they may be susceptible to predation
by other introduced reptiles, such as
Varanus indicus
(McCoid and Hensley, 1993a).
This introduced snake population has been the subject of scores of studies, and
early ecological research clearly ruled out a variety of other hypotheses to explain
the observed bird declines (Savidge, 1987a; Savidge et al., 1992). The dire effects
caused by this snake have led to a 14-year control program to prevent the species
colonizing additional Pacific islands, but indications are that Saipan may now be
invaded as well. If true, similar ecological effects may be expected there in the
coming decades (Fritts and Rodda, 1995; Rodda et al., 1999b).
The snake
Natrix maura
was introduced to the Balearic Islands approximately
2,000 years ago (Alcover and Mayol, 1981). It is credited with reducing the range
of the formerly island-wide endemic frog
Alytes muletensi
s to plunge pools in a few
steep-sided gorges in the uplands of Mallorca (Tonge, 1986; Moore et al., 2004a;
Pleguezuelos, 2004). It is also thought to have played a role in the extinction of the
endemic
Alytes talaioticus
during the Holocene (Pleguezuelos, 2004). Evidence for
these claims lies in the highly ranivorous behavior of
N. maura
, its absence from
fossils predating human settlement of the islands, and the persistence of
A. muletensis
at elevations where the snakes are scarce (Alcover and Mayol, 1981; Tonge, 1986;
Moore et al., 2004a).
The lizard
Anolis carolinensis
was introduced to Chichijima in the Ogasawara
(Bonin) Islands in the period from 1965-1968 (M. Hasegawa et al., 1988) and sub-
sequently released on Hahajima in 1981 (Miyashita, 1991). It has expanded its
range quickly (M. Hasegawa et al., 1988) and increased to tremendous population
densities ranging from 600-2,570 animals/ha and averaging 1,270 animals/ha
(Okochi et al., 2006). Feeding trials, direct observations, and stomach-content
analyses have demonstrated this lizard to feed on a variety of native insects
(Karube, 2004b, 2006; Karube and Suda, 2004; Makihara et al., 2004). Comparisons
of insect faunas on Chichijima and Hahajima before and after
Anolis
invasion, as
well as comparisons between these islands and nearby uninvaded islands, correlate
the decline or extirpation of several formerly common species of buprestid, ceram-
bycid, cucurlionid, and melandryid beetles; lycaenid and papilionid butterflies;
bees; and odonates to that invasion (Karube, 2004a, b, 2005; Karube and Suda,
2004; Makihara et al., 2004; Takakuwa and Suda, 2004; Yoshimura and Okochi,
2005; Okochi, et al., 2006). To date, toxic, nocturnal, and large, hard-bodied spe-
cies have not experienced catastrophic declines (Makihara et al., 2004; Karube,
2005). In all, at least 15 species of endemic insects appear to have vanished or
strongly declined because of the lizard. Most of these are small, diurnal, non-toxic
species with a fondness for resting on the sunlit vegetation favored by the lizards
