Biology Reference
In-Depth Information
competition has led to extirpation of
P. raffonei
throughout most of its original range,
and the species is now virtually extinct (Capula et al., 2002).
The replacement of
Anolis carolinensis
in Florida by invasive
A. sagrei
may be
due in part to competitive effects on reproduction. In enclosure experiments, female
A. carolinensis
laid fewer eggs when placed in sympatry with
A. sagrei
than when
housed alone or (sometimes) with conspecifics (Vincent, 1999). In contrast,
A. sagrei
females did not reduce reproductive output in sympatry with
A. carolinensis
.
Whether such results also obtain in the field remains unknown but, if so, would
complement the effects of hatchling predation by
A. sagrei
discussed earlier.
Concern has been raised about alien
Trachemys scripta
competing with native
Emys
orbicularis
in Europe (Frisenda and Ballasina, 1990; Servan and Arvy, 1997; Arvy and
Servan, 1998; Gianaroli et al., 1999), and they have been argued to act aggressively
toward the native turtle and displace it from basking sites (Kaltenegger, 2006). Cadi and
Joly (2004) demonstrated weight loss and reduced survival of
E. orbicularis
when con-
fined with
T. scripta
in outdoor enclosures in southeastern France. Data from these same
enclosures suggest this effect is at least partly due to superior competitiveness of
T. scripta
for basking sites, relegating
E. orbicularis
to poorer-quality sites (Cadi and
Bertrand, 2003; Cadi and Joly, 2003). This effect was not due to active displacement of
E. orbicularis
by
T. scripta
, but simply resulted from its earlier occupation of basking
sites during the morning and the reluctance of
E. orbicularis
to climb onto sites already
occupied. Competition for basking sites has also been posited as a likely impact
of
T. scripta
on native
Actinemys marmorata
in California (Spinks et al., 2003) and is
consistent with earlier data showing behavioral avoidance of the alien turtle by that
same population of
A. marmorata
(Holland, 1994). Impacts on wild populations
of
E. orbicularis
have not been demonstrated but may be feasible, considering the rare
status of that species in many localities and the densities which the alien turtle can attain
(Cadi and Joly, 2003). This supposition needs to be tempered, however, with recogni-
tion that
T. scripta
exhibits low reproductive success and juvenile survival in much of
Europe (Luiselli et al., 1997). If that observation holds generally,
T. scripta
populations
may undergo attrition as adults die but fail to be replaced by additional pet releases
because of the European Union's import ban on this species. So the practical effects of
T. scripta
for native turtle populations in Europe remain uncertain.
Enclosure experiments have also shown that female
T. scripta
gain a competitive
edge over native
Chrysemys picta
females in Ohio, United States, by being more
aggressive (McKenna and Tramer, 2001). Males of the two species did not exhibit
such differences. Growth of
C. picta
was not affected by this behavioral difference
but it seemingly led to an increased tendency of female
C. picta
to disperse away
from the
T. scripta
(McKenna and Tramer, 2001).
Vectoring Novel Parasites
The pathogenic fungus
Batrachochytrium dendrobatidis
induces a recently emerged
disease, chytridiomycosis, that has caused drastic declines and extinctions of many
