Biology Reference
In-Depth Information
(Karube, 2001, 2004a; Karube and Suda, 2004). Although preferred prey are small
diurnal inhabitants of vegetation,
A. carolinensis
has also been documented forag-
ing on large, hard-bodied cicadas, strictly ground-dwelling species, and nocturnal
species sleeping in leaf axils, with the last apparently leading to declines in some
nocturnal cerambycids as well (Karube and Suda, 2004; Karube, 2005). This switch
from preferred prey is thought to result from declining resources (Karube and Suda,
2004; Karube, 2006), and it is anticipated that yet additional insects will disappear
from Hahajima and Chichijima as more preferred prey species disappear (Karube
and Suda, 2004). Persistence of some of these endangered insects on adjacent
islands may be only temporary inasmuch as poor-quality habitat makes them popu-
lation sinks that historically were replenished by migration from the two islands
now having
Anolis
infestations (Takakuwa and Suda, 2004).
The related
Anolis sagre
i was introduced to Florida in the mid- to late-1800s
(Garman, 1887; W. King and Krakauer, 1966) and has rapidly expanded across the
state (Campbell, 2003a). During this expansion it has frequently been noted that the
native
A. carolinensis
has either disappeared or declined in numbers in many popu-
lations (Tokarz and Beck, 1987; P.R. Brown and Echternacht, 1991; Echternacht,
1999), and rapid replacement of that native by
A. sagrei
has been experimentally
demonstrated in the field (T. Campbell, 1999a). In highly disturbed habitats,
it appears that
A. carolinensis
can disappear entirely, but in more structurally com-
plex habitats it persists at lower population densities occasioned by its occupancy
of fewer, elevated territories than prior to invasion by
A. sagrei
(Echternacht, 1999).
Decline of the native appears largely due to predation on
A. carolinensis
hatchlings
by
A. sagrei
, with preference shown by
A. sagrei
for consumption of heterospecific
hatchlings over conspecific hatchlings in the laboratory (Gerber, 1991; Gerber and
Echternacht, 2000), and predation on hatchlings on
A. carolinensis
documented in
the field (T. Campbell and Gerber, 1996). Hatchlings of both species live near
ground level, thus bringing them in frequent contact with dense populations of adult
A. sagrei
(but not
A. carolinensis
) and making them susceptible to predation by that
species (Echternacht, 1999). The dense populations routinely formed by
A. sagrei
place the hatchlings of the sparser
A. carolinensis
in peril wherever insufficient
ground cover is available for refugia (T. Campbell, 1999a), and occasional con-
sumption of an
A. carolinensis
hatchling is all that is needed to severely depress
recruitment in that species (Echternacht, 1999). This appears to explain the
observed inability of
A. carolinensis
to persist in sympatry with
A. sagrei
in heavily
modified habitats lacking structural diversity.
The rapid spread of introduced
Anolis sagrei
and observed shift in perch heights
of native
A. conspersus
in the Cayman Islands (Losos et al., 1993) are likely
accounted for by similar dynamics. In that case too, laboratory trials have indicated
an asymmetrical preference of adult
A. sagrei
for consuming
A. conspersus
hatch-
lings (Gerber and Echternacht, 2000). This, combined with the dense populations
again seen in
A. sagrei
and the occupation by hatchling
A. conspersus
of lower
vegetational strata, would provide a similar mechanism for population declines in
the native anole (Gerber and Echternacht, 2000) as seen for Floridian
A. carolinensis
.
