Biology Reference
In-Depth Information
dietary competition (Klawinsky et al., 1994). Both displacement and dietary shift may
be mediated by interference competition for perch sites, which has been demonstrated
in enclosure experiments (Vaughan et al., 1996). However, in laboratory experiments,
Dame and Petren (2006) demonstrated that replacement of
Hemidactylus garnotii
across the Pacific by
H. frenatus
cannot be explained by either resource competition
or aggression, leaving uncertain what mechanism is responsible.
Clearer evidence attends the competitive exclusion of endemic and highly
endangered
Nactus
species in the Mascarene Islands by invasive
Hemidactylus
frenatus
. In this situation it is known that the endemic geckos
N. coindemirensis
,
N. durrelli
, and
N. serpensinsula
have disappeared across most of Mauritius and its
satellite islets, being confined (with one exception) only to a few islets lacking
H. frenatus
(Arnold and Jones, 1994; Cole et al., 2005). Outdoor exclosure experi-
ments have shown
H. frenatus
to aggressively interact with individuals of the
smaller
Nactus
species, displacing them from daytime refugia, injuring some indi-
viduals, and preying upon others (Cole et al., 2005). Competitive exclusion from
refugia presumably makes the native geckos more susceptible to predation by inva-
sive mammals like cats and rats, and injury is likely to directly impact survival of
affected individuals. The native geckos persist only in a few small areas having
substrates not easily negotiated by the alien.
The skink,
Cryptoblepharus nigropunctatus
, endemic to the Ogasawara Islands,
has been reported to be declining on Chichijima since the late 1970s, and by the
1990s the skink could not be found in areas having high densities of introduced
Anolis carolinensis
(Miyashita, 1991; Suzuki and Nagoshi, 1999). This appears to
result from direct competition with
A. carolinensis
. Where the two occur syntopi-
cally, there have been changes in substrate use and perch height by
Cryptoblepharus
,
suggesting that competition for favorable basking sites may explain some of the
native lizard's displacement. Further,
Anolis
were invariably observed to attack
Cryptoblepharus
when food was experimentally presented between pairs of each
species in the wild (Suzuki and Nagoshi, 1999). Both results suggest that interfer-
ence competition by the larger alien lizard is causing the decline of the native.
It has been observed that
Carlia ailanpalai
, introduced to the Mariana Islands,
is extremely aggressive toward the native terrestrial lizards, attacking them, stealing
their food, and possibly preying on them (Rodda et al., 1991; McCoid, 1995b). It has
been proposed that this aggressive behavior may serve as a competitive exclusion
mechanism contributing to the decline or disappearance of several populations of
native skink in the region (Rodda et al., 1991; Rodda and Fritts, 1992; McCoid,
1995b). This hypothesis is reasonable but has yet to be experimentally tested.
Podarcis wagleriana
is native to Sicily and the satellite Aegadian Islands;
P. raffonei
is a close relative restricted to some of the nearby Aeolian Islands (Capula, 1994a).
Podarcis sicula
is native to mainland Italy, Sicily, and Adriatic coastal areas but has
been introduced on some islands in the native ranges of
P. wagleriana
and
P. raffonei
(Capula, 1992, 1994b). In those circumstances,
P. sicula
either dominates or replaces
the native lizards. This has been argued to reflect competitive superiority because the
alien lizard predominates in virtually all available microhabitats (Capula, 1992).
Genetic (Capula, 1993) and distributional (Capula, 1992) evidence suggest that this
